in a young, active adult is typically caused by some kind of imbalance in the muscles/ligaments supporting the joint or by the consequences of an injury
that was not fully treated. For this reason, the best physician to see about treating these problems is an orthopedic surgeon
because he or she can do a more thorough history about the onset of the injury and the injuries that provoke it. In addition, a physical exam can help provide further information about what part of the joint may be causing the problem. Depending on the issue, physical therapy, steroid injections, or even surgery can often help fully correct the problem and get you back to the activities you enjoy without pain.
From your description, it sounds as though you may have some alignment issues with your knee. The lateral collateral ligament runs along the outside of the knee joint and helps provide stability to the joint. A strain or sprain or even microtear of this ligament could cause some of the pain and instability you describe. You may also have a problem with the alignment of the patella (kneecap). When the patella is overly mobile, particularly during activity, it can aggravate the underlying bone of the kneecap itself as well as the other bones that make up the knee joint. Strengthening the other muscles that help stabilize the knee can help keep the patella in better alignment and avoid the pain that comes with this kind of excessive motion.