Hi, I'm 20 years old and for the last 2 weeks have experienced frequent urination, lower back pain and pain when I press on my lower abdomen. I was first tested for a urinary tract infection which came back negative. Then my doctor suspected it could be Pelvic Inflammatory Disease, I was put on antibiotics and tested for STD's. My test results for STD's came back negative and the antibiotics are not making me feel better. My symptoms have continued. What could this be?