I'm not sure whats wrong with me?

First off, I'd like to say I'm 16 years old. I'm not currently sexually active. I have been diagnosed with rheumatoid arthritis. I have a problem with my upper abdominal muscles contracting constantly. For some reason my periods are very infrequent like i skip a month or two and once i went a whole 7 months with out a sight of blood. Recently, while not on my period, I felt extreme pain in my stomach. It went on for about a week before I went to the doctor.They told me I didn't have a uti (which is what i thought i had) and they said i had a very high white blood cell count which meant i had some class of infection, just not a uti. I started my period monday morning and the pain is double what it has been. My period cramps have always been extremely bad, but this is way worse than usual. My legs feel like jelly. I can't eat. I have nausea. I'm so freaking tired even though I go to bed at reasonable hours. I've also been told by my doctor that I may have fibromyagia or something, I have no clue what that is. But uh, if you know/think you know whats wrong with me, please share because I feel like crap.