120MG a DAY??? That is an INSANE amount of prednisone.
At the height of my disease, in the hospital, the most I was ever on is 80 - that's NUTS. That level of pred, on an ongoing basis, can cause adrenal dependency and all sorts of badness.
You need to find another doctor. Stat. You are clearly in a major flare, and you need to find a doctor who will work to get you back to normal. Despite your lack of insurance (get insurance - if your parents have insurance they can cover you until you're 26 per Obama's new healthcare regs), you are probably in the neighborhood of needing to go to the hospital.
While in major flares, my doctor prescribed Vicodin, and I was on heavier painkillers at the hospital - but it is NOT a long-term solution. You need to find a way to get this under control.
Have you tried the specific carbohydrate diet (SCD)?