Suggest Remedy For Persistent Vomiting

I have a 2 month old boy that weight 10lbs 13 oz at birth. At almost a month old he started throwing up real bad and a lot. We took him to the Dr. numerous times and we changed his formula a few times as well. He has been on Infamil Lipil, Enfamil Prosobee, Enfamil Gentlease and he is currently on Similac Alimentum. Changing his formulas has not made a difference at all. He lost 1lb 5oz and the Dr. decided to put him on Zantac for acid reflux (even though they re not sure that is what is wrong). We went back the following week because it hadn t made a difference and they put him on Prevacid and Zantac. Prevacid in the morning and Zantac at night which seemed to have helped for 3 days. The fourth day he begins throwing up again. We have took him back to the Dr. 2-3 times a week for the past 2 weeks for a weight check. He did get back up to 11 lbs 14 ounces. So a few days ago I noticed that he had brown pieces of something in his throw up and had been watching it. Yesterday all he was throwing up was brown. Looked like used snuff that my grandma use to use. We took him to what is supposed to be one of the better hospitals in the area last night and after doing blood work, catheter and x-rays they cannot tell us what is wrong. At the hospital they weigh him and he has lost 4 ounces in 3 days and it seems that he is keeping absolutely nothing down. He only eats 2 ounces every 2-3 hours.