My son has a pimple that looks like a mosquito bite that got infected. the area is very itchy and painful. 4 days now?

Pustule: Apply warm compresses. Apply an antibacterial ointment like bacitracin after patting dry. Cover with gauze and paper tape. An early boil or abscess may be forming. If spreading redness occurs oral antibiotics are needed. If swelling and tenderness worsen, the pustule may need to be drained of pus. See a physician for evaluation if no improvement with warm compresses.