Help please! My son has a stomach virus for a month now. He hasn't been eating well or at all or point he's not taking…

Help please! My son has a stomach virus for a month now. He hasn't been eating well or at all or point he's not taking lots of formula anymore. I don't know what else to give you and I don't know what to do at this point, today he woke up crying nonstop I'm guessing because of pain we try to feed him he didn't want to eat anything. I'm not sure what to do at this point I have took him to his doctor the hospital him he's been on medicine and nothing seems to work I'm thinking of taking him today to a hospital that's just for children. Any suggestions on what I should do any advice please help me!