I take prednisone , 15 mg and have been on it for 6 months..?

I've been on Prednisone several times, but never for more than 3-6 weeks. Time to get a second opinion.

Talk to your doctor as soon as possible.  I have heard of the condition before.  I was on heavy doses of prednisone ( 70 mg/day ) for four years and never had hip or joint problems, it about drove me crazy mentally though.  My doctor was finally able to wean me off of it when my condition changed ( sarcoicosis ).  Talk to your doctor asap, Good Luck.

I've been taking prednisone for quite a while for my rheumatoid arthritis.  It helps with the pain a lot, but after taking it for a period of time, you body may build an immunity to it.  Try taking aleve for a few weeks, then switch back to prednisone.  Aleves active ingredient is Naproxen.  It's an anti inflamatory that works well with any kind of joint or bone pain.  after that, switch back.  You won't want to increase your dose of prednisone without your doctors consent.  If I were you though, ask your doctor if there is anything else that you can take instead of prednisone.  As I said before, it works great for pain, but there are a lot of side affects that can be associated with it such as moonface, necrosis, and even diabetes.  
P.S. Its not going to be easy to ween you off that stuff though.  You cant suddenly quit taking it.  If you do, you may experience flare ups with your pain.  Ask your doctor for information on how to get off it.

It's best to see your doctor.  long-term steroid/Prednisone use can hide other health problems and weaken your immune system.