Rash after iron supplement

Has anyone seen this before? I left word with his pediatrician but they haven’t responded yet because of the holidays. He hasn’t had any new food, or come in contact with any new soap or lotion. The rash is on his front, back, arms, legs, neck and face. It is not on his scalp, hands, or feet. The only thing we can think is that it was caused by the iron supplement his doctor prescribed him which he took for the first time yesterday morning and the rash appeared shortly after. He isn’t itching and doesn’t have trouble breathing. There is no fever and the spots fade with pressure. But it’s been over a day and, although they have faded, they haven’t completely gone away. Does this sort of thing go away on its own? Should I just wait for the doctor to get back to me?