It sounds like bursitis. I have had it on and off for last 15 years, I was about your age when it started. At its worse I couldn't even dress my bottom half in the mornings and had to have steroid injections and even surgery was considered. Over the last 2 or 3 years it's got much better but I still get the pain if I lay too long on my hip and for about an hour after waking. I find if I get up when the pain starts and walk about a bit then go back to sleep it's not so bad but if I stay in bed for more than 7 hours it's terrible. Bursitis is mainly caused by uneven walking, carrying a heavy bag on one shoulder for example can cause you to walk unevenly as does cross country walking or running (the cause of mine), some people even have one leg slightly shorter. A 'bursa' of fluid develops at side of hip, mine was so bad I could actually see the bulge. If its Bursitis it will feel tender when you press on this area .
All I can say is that you kind of get used to the pain after a while and as long as you don't overdo it and keep moving it does get better.