My Son Has Had A Bad Upper Respiratory Cold. He

My son has had a bad upper respiratory cold. He also just recently was diagnosed with allergies to food. He had blood work a few months ago for immune disorders, etc. Everything was fine so they determined it was food.
Last weekend he did a one arm pull up and a bunch of pull ups with both arms. His arm was sore for a few days. His arm is now sore in the armpit and causing pain, it has a hard lump deep inside to what he felt, i thought it felt more like a tendon swollen or something else. Of course he knows his body more than i do.