Hey sara,
i'm 26 years old, when I was 15 I too had pins put in my hip for the same reason you did, slipped captial femor epithsis, the pain settled down for a number of years but never went away, when I was 17 the hip pain got worse and worse, I dealt with it for years as my doctors put me on all kinds of pain medication, tryed injections in my hip etc.. My hip now had severe artiritis, the doctors did a scope and a scraping of the hip and found out I had no cartdledge. Finally two months ago I got the total hip replacement, I still have pain but its different kind, remember i'm only two months out from my surgery so i'm still healing.
I knew my hip needed replaced when the pain effected everything in my life, I could not sit for a long time because of the pain in my buttocks, when I walked it hurt alot, I limped and could not sleep on my left side.
Bottom line is this, I had close to the same problem as you, it got worse until I got the hip replacement. Not to worry you because its not that bad, a hip replacement may be in your future, just hold out as long as you can and visit an ortopedic to see what they can do to help deal with your pain and slow down the process.
Your going to hear doctors telling you that your too young to have any problems, just look at this message board, as you can see being young has nothing to do with it, and take it easy when your having sex (but still have some fun)
if you have any questions feel free to contact me.
Good luck,
jason