I am 18 years old and I have been on the NuvaRing for about a wee...

I have been getting the same thing in my butt cheek.
Im not an expert but i think its something to do with a trapped nerve in sciatica (not sure i have spelt that right) its really funny as i have just started getting it again as im typing this!
You might be carrying stress in your back from all the stuff on your plate.
Go see a chiropractor.

I also have experienced trouble sleeping when I went off and then back on the Nuvaring. I had no reason to be more stressed than usual, in fact, my classes were the easiest they've ever been. I also have the vaginal burning after sex and irritation that can last for days. It's not good. The sleeping problem did go away, however, I am still trying to determine if i want to change birth control methods, or try to wait out the painful and itchy irritation.