3rd Rash in the last 6 weeks

This is the 3rd rash my son(11M)has had in the last six weeks. First time was similar but worse, thought was poison ivy, prescribed prednisone. Second time, 3weeks ago it was different, red spots on back, neck, lower face, Chest and arms. Doctors said it looks like an allergic reaction. 3rd rash which he currently has hurts a lot, paediatrician thinks it could be a symptom of walking pneumonia, waiting for test results for that. We are being referred to a dermatologist but would like input if anyone has seen these types of rashes before?