Extreme unusual pain on period??

I'm 15 years old and I've never had sex. I've had regular, normal not very severe periods since I was 11. But in the past couple of months, the pain has become absolutely unbearable. I don't mean cramps or back pain or bloating, this is a completely different pain. It normally starts out with little prickly pains inside my uterus but then it moves to everywhere else and gets more severe, especially around the upper uterus/ovaries area. Everything outside looks as it normally does when I'm on my period. But when I use the bathroom, I'm brought to tears nearly every time because of the burning and stinging it causes down inside there, and I can hardly sit down comfortably without having to stand up quickly to avoid the pain. Everybody from my school nurse to my normal Doctor is shoving it off as minor cramps and saying I'm overplaying it but that is definitely not it. I haven't been able to go see my OBGYN, she always has full appointments or I have important things to do when she has an opening. I finally got an appointment on next weeks Monday, but this pain is intolerable and I have to know what it is. Does anybody have any idea what it could be? Please and thank you😌