I'm not quite as young as you (I'm 46) but it took about 2 1/2 years for the doctors to even think about arthritis in me. They have no idea why I had osteo arthritis at such a young age but the disease is in both sides of my family. I had all sorts of gynocological tests on me, chiropractor for a year, etc...
I think the hardest part is not knowing what the cause is. If they are sure that it is bone on bone, there is not much you can do aside from a THR (total hip replacement). You can put it off, but you are too young to be able to put it off for long (maybe a year or two if it's already at the bone on bone state). The limits are sooooo different for different people so it's hard to counsel you here, but I think everyone agrees that the hip pain you are having now goes away!
Just to give you an idea... it has been 5 months since my hip replacement and I can do everything that I did before but just a little slower (I'm still getting more stamina in the muscles and working on the healing process). I can bike, walk, get down on the ground and garden, do pilates and am almost to the point where I can go back to a kickbox class (it's moving a little too fast for my new muscles to keep up, but I anticipate being able to do it within another month or so). My flexibility is extremely better. I no longer hurt when I sit in a car (the pain used to go down my leg and ache in a car). I also did TaeKwonDo (I'm a 2nd degree black belt and instructor). I still teach and I can do the TaeKwonDo but I'm not sure about breaking boards and sparring... maybe that will be a limit.
Anyway, I just wanted to enjoy my son (he is 12 years old) and be able to participate in family activities again without having to sit out. I can do all that now (and more than I thought I ever would).
I hope I answered some of your questions... always ask everything you can and find out whatever you can. It's a wonderful surgery but it's also permanent. I hope you feel better.