Could Pain, Swelling, Weight Gain, And Other Issues After Septic Arthritis Indicate An Underlying Condition?

My son who just turned ten recently had a very severe case of septic arthritis in his left his which resulted in two surgeries and over a week in the hospital and possible a vascular necrosis. This happened all in early October but I’m concerned because he has not been feeling well ever since and has had a lot of pain swelling and stomach problems and noone is doing anything he recently had some greasy oily stools and now the veins all across his lower back are becoming very pronounced and he has gained 30lbs since October despite constantly increasing activity levels and physical therapy and is constantly getting washed out pale face and feeling like he is dizzy and short of breath at times my worry is could they be missing what caused this to happen or could there be something underlying I just want my son to feel better.