Is Is Perthes Disease Or Arthritis Causing Pain In My Legs?

Hey, Im a 18 year old girl and i have had perthes disease since i was 3yrs old in my left leg. The pain is much worse than it was after i had to wear braces on my legs. I can't sit or lay for a long time and i can't cross my leg. theres pain when i just relax and when i do exercise.. The pain is that extreme that it makes it uncomfortable to get to sleep sometimes. The i've seen one doctor that says i have arthritis. I don't know what to do to make the pain go away.