Advice

My 3 yr old refuses to eat. He has been this way since birth.. he has been looked at by a gi speaclist a nutrisonist and his regular doc.. the only thing they found was avid reflux and he is on zantac 2 times a day. And has been for more then a year now. He only ways 28 pounds. I have tried everything.. today he has ate half of a sausage biscut! He is on pedia sure 3 times a day... idk what else to do.. he throws a fit when you try to get him to eat.