The bug always seems to happen at any stage of the game, and in all new playthroughs as well
Pain killers: Works as you would expect (takes your money, reduces pain, and can't buy them if you don't have the 20$ asking price)
Massage Oil: Doesn't take your money, but does increase belly capacity, but only can buy as many as you have money for each day, before it stops increasing belly capacity. (ie. if you have $20, you can increase you belly capacity twice that day, before it stops increasing it anymore, BUT you will still have $20 after those 2 purchases, that you could spend on a pain killer if needed, or keep for next day to use for more massage oils then, if you have $1000, you can get it 100 times, so on and so forth)
Scented candles: Does not work AT ALL, doesn't take your money, and doesn't reduces stress. However if you do attempt to buy as many (or more), than you would be able to afford that day, it does block you from buying the Massage Oil, so seems like they are being bought with the same pool of "phantom" money as Massage Oil, just not having any effect
Hope this formatting and more detailed info makes it a bit easier to understand, and keep track off