So I'm extremely confused I have been having unprotected sex because I want to have a baby and I am nauseous and bloated I was having intercourse tonight and I was on top I went to sit up and I feel a lot of pressure and hurt extremely bad why did this happen

Could have been the position. There are a few conditions of the uterus/vagina that can result in pain with sex.

Dozens of medical reasons, or just position, lubrication issue and more.
If you and your partner are wanting pregnancy, you need to be tracking your ovulation medically (not with online charts) and timing sex properly.