Here's what all the pills do, if it helps.
Power Pill: Has different effects for each baby, but mostly boosts their power.
Speed up: It does increase the speed of babies, you probably just can't notice.
Speed down: is a negative pill, like the ones in Isaac.
Percs!: Gives a shield to a baby, that can take extra damage, as well as block instakills (same as Book of Shadows)
Something's Wrong: Causes a baby to shoot a random tear from a pool of all tears in the game (except crispy baby shots because of a bug). Best used on brother bobby.
Full Health: Self explanatory.
All the pills other than something's wrong do work on heart producers, including power pills, which make them give 75 hearts.
As for shops: In my experiences, I have actually almost always had over 100 coins, especially on the first floor. Assuming you keep all chargers (which you should on the first floor), you will get 72 coins from them. Then, you get what seems to be about 20-25 coins from the boss. This should bring you to over 90 coins. The fact you haven't had enough means you probably haven't picked up coins on the floor, either because you haven't noticed them, or because you've gotten extremely unlucky and none have spawned. Coins can drop from poops, enemies, and three drop from yellow champions, and coins can be pennies, nickels, and dimes. You would need to get 2-7 depending on which of my estimates for boss drops are right.
Getting a 99c item may not always be the correct choice anyway. For instance, due to only one negative pill currently being in the game, Phd is pretty unhelpful.
I hope this helps!