Pain w sex

Last night I had sex with my long-distance boyfriend for the first time in about a month. I was slightly ~drunk~ but absolutely consented. Here’s my concern.

Sex has never been painful for me. A little sore when we’ve gone a while without seeing each other, but just for a minute. For some reason though, last night when I got on top, it HURT. Like, to the point where I had to get off. Him on top was fine, but when I was on top it felt like my whole abdomen tightened & got super painful. He’s definitely not small, but like I said this has never been an issue. Anybody know why this might happen? Should I be worried?