Pelvic pain/uterus pain:(

I've been off of birth control for 5 months and I've gotten my period twice, I tested positive for ovulation the 1st of december, I've taken test and their negative my uterus has felt like I can't relax it like tense , during sex tonight I was on my belly and it was hurting pretty bad and when we were done it felt way more tense . I'm not sure if this is cyst or if this is my appendix ? Please help