Hitting my cervix?

So my boyfriend & I had sex. Twice today. But the second time i was riding him and I started getting lower abdominal pain. As if i was having a period cramp. Which i wasnt. This never happens. He was going pretty deep. What could this be?  We looked it up and it said he was hitting my cervix. Another page said it was just air & heat trapped(Fyi, when he put it in it wasnt wet enough)