What Causes Pain In Uterus?

Hi. I have a question. Okay well first I'm 22 and a virgin. I only really get my period once or twice a year. I just had it in the beginning of January but I noticed that it hurt a lot in my uterus section. I noticed now that my uterus still hurts...even more when I have an orgasm. I don't put anything up there but tampons when I get my period. Do you know what could be wrong?