There is something funky with the RNG in this game. I impregnated Chitose and Saya at the start of a Resort vacation but every single other girl I tried to impregnate even with the +8% drink failed even using all 190 stamina. For shits and giggles I save edited my stamina to max and it still failed over 90 attempts in a single session. I figured it may just be that it determines Fertility at the start of a resort attempt so I returned and even the regular girls aren't getting pregnant no matter how many attempts I use.
Just to test it I paid the 10 million credits to fuck the Fertility Goddess herself who always has a maxed out 99% chance and even THAT failed multiple times before finally succeeding. Any idea if I fucked something up? Reverting to a previous save doesn't seem to help and other than altering stamina that one time I haven't fucked with any other aspects of the game.