What could this be? Leg pain since childhood

I have had chronic leg pain since the age of 5 or 6. The pain is sharp and strong, not throbbing and happens in my hip and knee, sometimes just one or the other, sometimes both. It feels like it is in the centre of my leg, straight through. The pain has also been known to reach into the thigh and lower leg, though this may just be radiating from the joints. It happens in both legs but never at the same time, it seems to alternate between the two. There is no pattern, though when I was younger it happened more at night. Now (I'm 20) it happens equally in day and night. The pain is not helped by heat or cold, and does increase a bit with movement, though sometimes movement makes it feel batter. I get the pain at least once every 2 or 3 weeks, sometimes more or less. My doctor seems to think it is "growing pains" and will go away when I am 21, though I have not grown the slightest in 4 years. I can still walk but will limp slightly and it is difficult. I sometimes take ibuprofen which helps off and on, sometimes it does nothing at all. When I was younger it would wake me up at night, now it distracts me from work and keeps me from falling asleep. My daily activities are only mildly affected, though I do have trouble with walking and doing errands and going to class. I have been dealing with this but would love some relief! Thank you!