I'm guessing this is due to Womb of Lust, which resets when you do a H-scene or use a Blessed Water, giving you back the WL it was suppressing. In that case, it's why I said you should not be affected by WoL when you start a pink H-scene chain with hydrangeas. If you got 10 more willpower than you expected, it's probably 2 days' worth of WoL. You can check it in the menu under Skill -> Curses.
As for the difficulty, this is a situation where the dev balances the game for Normal and doesn't really test Hard afaik. No shame in playing on Normal.