What Could Chronic Pain In Kneecap, Thighs And Hip With Weakness Indicate?

I am 20 years old, and I am having pain in my left knee constantly. The pain is below and above my kneecap, also underneath the knee cap, my lower thigh, left and right side of the knee, behind my kneecap on the outer side of the thigh, in my hip and butt, and in my upper calf, to the outside of the shin. I've researched my pain and have seen a couple answers including IT Band Syndrome and Patellar Tendontitis. Any clue what this could be? I've taped my knee for about 4 years when excercising and it helped a lot until now. I'm using KT tape to help with the pain and it seems to be helping a little. But I hasn't got the taping down pat. My knee does not feel supported enough. I work at a watermark where I walk for 10 hours every day. I was also a competitive gymnast for 16 years. Please help!