My son has this rashes. He is quite irritated by it. Any idea what is it? Do I need to see a doc?

This looks like Roseola Rash. Does he also have fever ? It is mainly caused due to a herpes virus so you might want to take your son to the doctor. Also give him a lot of fluids and sponge baths. It will disappear in 2-3 days. there is no particular treatment for it but the doctor might prescribe some antibiotics