Going by what you've said here, I think the issue is you keep doing combat related things. Combat is the absolute LEAST profitable thing you can do in this game even if its (almost) the only way to do fighting guild stuff. 

Try out a playthrough where you start your main character, as well as your starting servant out with maxed Charm and maxed Sexual. You can even give him the Curious or Teacher trait to help even more. MC starting class doesn't matter. You can also set the race to one of the Beast races for an easier start. These will do a few things for you: 

1. Your main characters Charm Factor (IE the poor -> good -> great etc) will give you higher rewards from quests and also increase the amount of Dates you can do. This is important since Dates can increase your characters Physic / Charm / Wits, can help with obedience / loyalty / authority, and can lead to sex after the date which bypasses the normal limit on the times you can have sex per week.

2. Your main characters Sex Factor will increase the amount of times you can have Sex per week. This is significantly less helpful than the Charm Factor, but will help early on with increasing sex skill which affects how much you make through prostitution (which is our main source of income in this route)

3. The Teacher trait would help their partner gain sex skill faster, this is particularly useful on the Main Character since all dates go through him, and dates can lead to sex. The Curious trait gives you more exp from sex, and going by what I just said about dates....its very useful on the Main Character.

4. The reason I recommend one of the Beast races (Particularly the fox) is their access to the Natural Pet class, which gives better bonuses than the normal pet class and is VERY easy / quick to unlock.

Now starting out you immediately side with the Servants Guild, get your first servant, set them up similarly with the master while setting their TAM and TMD at similar levels with TAM slightly higher.  Also give them Curious over Teacher, and start them with the Harlot class.  The first thing you do is equip the items you got from the servant guild, check the shop for any charm increasing gear (last tab on the right). Try to get the gloves, ears, underwear, and maid outfit if any of them are available, but be aware at the start you only have 500g. Put both characters on Prostitution duty immediately but be sure to do a date before passing a day. The goal of the date is to raise consent, so pick praise first, then pat head, comb, hug, kiss, flirt, intimate talk, then spam hug. Chances are the first one will end without sex, which is fine. You can use the Praise skill from the hotbar afterwards to further increase consent and the next date will almost certainly lead to sex. 

Now pass a day and then date again, this time do not use any affection options, immediately swap to training and click Practice charm. If you maxed both characters Charm Factor out, they will gain 15 charm this is super important since charm increases the money you get from prostitution. After the date the character will likely want sex basically always do since it will usually max the characters Lust bar afterwards which will give you fuel for abilities later. If its boring to go through the same menu a lot then during sex click on any character thats not your main character (or all of them other than your main character if you have more than 2 participating) and click "Let X lead" Then you can spam click observe in the bottom until the 20 turns are up.  If at any point you get enough exp to add a class, make sure you put Harlot on the MC asap.

You'll want to repeat that till you are out of dates, though make sure you check the store for charm increasing gear at least until you have both characters kitted out. At no later than the 3rd day make sure you check all the quests to see if there are any you can complete easily. Any quest that asks for food, literally just buy it from the store. Because of your maxed out Charm Factor you will almost always get more money back from finishing a quest than you spent on buying the quest item. If theres a worker quest that asks for something like "an axe with a bone blade" You can check the shop each day for one, but if there isn't one in the shop just don't accept the quest ever. If theres a Servant quest make sure you read the quest carefully to see if they are asking for a worker or asking for a slave. Be very careful with these cause if you mess up and give away one of your better workers on a slave quest then they will be gone FOREVER. These quests will usually ask for something with "Charm 33" or "sex skills 25" or TAM / TMD at average, you can just look through tows market or the guilds and buy the person who meets the requirements and instantly hand them over. If its a charm one then you recruit someone who has a decently high charm factor then raise their charm skills through datings "training" and hand them over when they meet the requirement. Same goes for the ones that need sex skills. Then theres the mages that generally have the easiest quests as most of the consumables they ask for are in the store on one day or another.

Eventually (usually after the first week, or after the first bank payment) You'll want to recruit more characters. The important thing to note when adding more characters is to aim for high charm factor, sex factor, and TAM / TMD not too low. The reason for this is the classes you'll be aiming for will require it. Speaking of the classes you want basically anything that adds charm or value from prostitution. Harlot,  Pet / Natural Pet, Bard, Dancer, Incubus and the Servant Guild classes are all things to aim for. Also be sure to buy food occasionally for your people, and in between bank payments make sure you buy the materials required for the Mansion Rooms / Luxury Rooms upgrades. The former so you can recruit more people, the later so you can max out their loyalty then put them in a luxury room and set them to "Coerced Labor" which becomes a free 15% production boost. If you are willing to buy more food, you can also set extra rations for another 15% boost. Oh and after you buy the upgrades remember to set someone to the "upgrade" job till its done or you won't get it.

Honestly if you even just loosely follow this mini-guide you'll easily pay the bank off in full. And likely won't even need to since you'll finish out Servants very quickly, Mages very quickly, Workers somewhat quickly, but never Fighters (you only need 3 anyway).

Jeez that was way more typing than I intended to do, but here you go. Just gotta understand the games systems and its really not that hard. The moment I noticed how god awful the rewards for combat were, and ignored it completely, I stopped having any problem getting money in this game.

Notable mention for Fairy, low mana cost for 50% heal is great for salvaging 'oopsies' during questing, especially if you built an HP tank.