Pelvic ache for 2 months 19 yrs old?

Hi. Ive been having this pelvic ache on my right side for 2 months now. I havnt gotton my period in about 2-3 months and it has been trying to come(ill spot for a day then it goes away) this is due to my medication Invega. Cause this pelvic ache be from not getting my period for so long?Almost like my body is trying to make it come but its not coming? Ive had this ache a few years ago but i fully got my period and it went away the day I got it. Now Ive been to the doctors 2 times, I thought it was a uti, was on 3 weeks antibitoics and they didnt work, my culture came back negative, no uti. What could this be? Im sooo scared and upset.