Are you playing on easy? If you want so see sex stuff, play on hard. But as an example. If you want early vaginal Sex, you need high Pussy and Cock Desire, your Character needs to be wet, your character needs to lay on the floor and lose her clothing and the opponent needs to be a Thug that has a errection (red face). You can get Sex Day 1 with that. But remember, that turning her to fast into a Slut, makes the game early almost impossible.
And you unlock Sex Skills, after the prisoners to a certain action against you often enough. Like getting kissed often enough, unlocks kissing as an example.