Hi, J.. I'm in Provo, FYI. He is at a growing age. If you're really worried about rheumatoid arthritis, just see your pediatrician. It truly sounds like growing pains. My son was miserable with that pain for 3-4 years, and then we found a wonderful calcium product called Nature's Life Calcium, Magnesium and phosphorus liquid. It comes in a quart bottle and lasts forever. I got it at Good Earth.
I would hold Jake with my hands on his knees (after I wrapped them in socks), and we'd cuddle on the couch. It was a wonderful, sleepy time, but we'd have some mighty good talks during that time. Within 20 minutes, the cramping would stop and I'd tuck him back into bed. The times between get longer, and then kids learn to handle the pain, or give some ibuprofen.
Good luck!