Coldsores in a 11 month old baby

Ok this is day four of my baby boy of having coldsores all around inside his mouth.. he haven't ate food for three days and barely drinks. I took him to see our doctor yesterday, she didn't give him anything to treat it but said to give him advil and cold things such as ice cream, yogurt, and freezies but we already been giving him ice cream and yogurt. Today he refused to eat now, as he just cries whenever i try to feed him. Now I notice he's getting sores on his face also he's very tired as he wakes up crying because of the pain, i would say he only sleeps for like 15-20 minutes and stays up for abit and goes back to bed.. anyways im just wondering if any you mommy's have any advice and how did you cope with your little one with coldsore and how long did it lasted for?