My son is 7 and has te exact same thing...leg pain, stiffness then within 48 hours has a respitory infection. We have been to rheumatologist, nuerologist an now being referred to orthopedic. Please email me jlzaller @ gmail *******
I can understand your concern and as he has been sick so much I feel you need another opinion,this has been a strange past year of sickness both for children and adults, you may want to ask about allergies especially environmental ones.He may also have growing pains, many children do have them we see a lot of it on this forum.The description of symptoms also copuld be from the flu like' sickness that has been going around that the doctors have no answer to yet treat with anti biotics ..I would make sure he is getting plenty of fluids, ask for something for his cough, he is 5 so there may be a med to give him.Let us know how he is doing ..