I would agree Eeyore888 on this one. An pelvic ultrasound is a good place to start. Pelvic congestion could be a possibility due to collateral veins filling with blood and pressing on the bladder. This condition is also known to cause irregular menstrual cycles. Of course I'm not a doctor or a woman but I have had pelvic congestion and it's unlikely that what you have is an STD that is causing your problems.
It sounds like you have some sort of reproductive problem. I don't mean to offend you, but it could possibly be an STD or it could be something like endometriosis or fibroids. You should see a gyno and have them do some tests (pelvic exam, ultrasound, etc.) Missing periods at your age is definitely not normal! Best of luck and hope you feel better!