B.R.
Our son grew 6 inches in 6 months a few years ago. On the advice of our pediatrician we took him to see an orthopedic surgeon. Our son had/has Osgood Schlatter. The dr told us that our ds had to stop all physical activity, aside from walking to and from the bus stop and around the school. After that period, he was permitted to participate in gym class as long as his knee was feeling ok and had to discontinue all sports for 6 months. Three months after our initial appt. he had a recheck. Because we actually did what the dr. suggested the Osgood Schlatter was healing faster then the dr. said it would. The dr. stated that most kids won't do what he says and they don't heal as nicely as our son. The inflammation was so bad for our son that the lump from the OS was larger than his kneecap...it looked like he had two of them. Its been 2 years and our son is mostly pain free. He uses a knee brace during conditioning for wrestling when he feels pain.
You might want to think about seeing an orthopedic surgeon since this is their specialty. I hope your son feels better soon.