I’m so sorry to hear this. My son is also afflicted with leg pain (ankle, shin, knee). Here’s a short video when he was symptomatic:
My son has multiple allergies. His diet consists of 6-8 foods. This video was taken during an 8 month dairy trial. Upon removal of dairy his symptoms of pain and fatigue progressively improved!
My son was recently diagnosed with MCAS. For him pain can be a “symptom” of a reaction. Specific triggers like dairy, banana, strawberry, latex, and chlorine will cause him pain flares. I’ve found Diphenhydramine (Benadryl) to help alleviate his pain. Continual doses round the clock usually do the trick. I’ve also found that an adult foot bath with warm water and bubbles help as well as cartoons for distraction.
My son is about to start Gastrocom which I’ve been told by his doctor should help with the pain.
Good Luck. I know how hard it is to watch them in pain. Please keep us posted.