What Causes Pain In Knee And Hip Joints?

Hi, I have been having pains in my hip and knee joints. At one point, my hip was hurting so bad I had to walk on my tip toes to ease the pain. The pain is usually in left leg but occasionally its both. It has been going on for a while now and usually it would pop up once a month or two but lately its been getting worse and popping up several times a week. Its not all the time it just starts and lately its been worse and worse. The pain kind of throbs and when it comes I usually limp or walk differently it feels like something is out of place I guess.. It can last from a couple hours to a couple days. I don't know if anything in specific triggers it because its very spontaneous and there's no specific pattern I recognize.But I have cheered August-November 2009 was constantly tumbling but I haven't had an injury that I can think of that could have triggered this. My parents write it off as growing pains but do you have any suggests of what it could be and should I see a doctor? Could it be something serious? I really need answers.