Found a bug. Minor spoilers ahead.
After finding Cassandra's Locket, and doing some story-related stuff to it directly, you can find the original again when searching the cabin.
Would also like to suggest that Clara's Doll simply zero out your horny meter. It doesn't use up any time, so you can basically reuse it multiple times with no penalty. Alternatively, it just costs 1 minute to use. I prefer the former, but for balance the latter is probably better.
I've also noticed that the Boob Potion doesn't seem to actually change your size at any point. If this simply requires multiple uses, that would explain what happens. Although I wouldn't mind a secret maximum size that only happens when the boob potion is used at the largest size Cassandra will get you to.