Pain after sex

My boyfriend and I are in a long distance relationship and started having sex in August of this year. Then after leaving for college we see each other about once a month and do it then too. In the beginning of December I went to go visit him and we did doggy for the first time. (We’ve only done missionary and cowgirl before this) The next morning we tried to have sex again in missionary but it hurt so bad for me that we had to stop. Now almost a month later we are both home for Christmas break and we were going to do missionary but I still had the pain from my vagina just not as bad. It doesn’t hurt when being fingered or anything else just sex. We don’t use condoms because I’m on the depo shot and he pulls out. We haven’t slept with anyone else and I’m always aroused when we do it.

Has this happened to anyone else and how can I make it better?