My hip and right butt cheek hurt, why is it?

I used to run a whole bunch and never had a prob. I stopped and gained a bunch of weight. Out of nowhere i feel sharp pain and makes it hard to walk let alone stand. Is it cause I'm not active anymore? I'm 21, 5"10 used to weigh 150 now the scale lingers around 200. Haven't had time to go to a doc so if I really need to, I will. Any advise is appreciated.