HELP! Many problems starting with lower back pain

I have felt fatigued all school year and i have no idea why. I also have never gotten a regular period and i am now 19 and have had it for 6 years now. About three weeks ago I started having terrible lower back pain, which caused nausea. I went to the ER 4 days after the pain started because the pain became unbearable and i had a rising temperature of 101. The hospital also did a pelvic exam and a UA and said my cervix was extremely inflamed and the pain during the exam was unbearable for me. They treated me for a UTI and PID with oral antibiotics and tested me for an kind of STD (which i am clear of) . After i was finished with the antibiotics i went to my primary care doctor for a follow up and she gave me muscle relaxers(for the back pain) and something to bring down the inflammation. I also got blood tests for Lymes Disease, Mono, Thyroid, Liver and all that came out regular. I am still experiencing lower back pain, fatigue, and pain with insertion of tampon and during sex. I am also still experiencing a low grade fever once in a while too. If anybody know whats up with me, or have had a similar experience I would love to hear!    

[remar]

PID can be hard to treat. When you went back the second time did they do blood work to check your blood cell counts? That would show if the infection and inflammation is still going on.