ive done that but they wont let me do it if i try to attempt that
Did you check their patience bar? Every time the amount reaches 500, 1000, 1500, and 2000, their patience bar drops quite a lot, unless you've increased their obedience and corruption stats. These two stats together make the patience bar rise, preventing it from reaching 0
If the patience bar reaches 0, you will no longer be able to have relations with that NPC until the next day
It's also important to note that, randomly, the characters can have a rejection to creampie and cumflation, which is why their improvements can take longer