i feel terrible abdominal pains and cramps during sex?!

Sometimes you will feel pain or cramp in your lower belly during sex, due to your partner hitting your cervix too hard. This happens due to him going inside you too deep and too hard/fast. Tell him to be more gentle, or try other positions which will restrict him going in too deep. See your doctor if it still persists.

see a doctor. Seriously.

Since you're a guy, why are you posting in "women's health?

See a doctor, this could be an std

I'd go see a doctor