Was Wondering I Have A 4 Month Th Old Baby

was wondering I have a 4 month th old baby at home he has been throwing up everything (Pedialite., formula, and even water) this had been going on for about 4 days now.
On the 2nd day I finally figured out a system that would work. I can only give my son half an ounce ever 30 minutes. If I feed him anymore than that no matter what he will throw it back up. I have been to the er 2x and seen his primary Dr. All in witch are completely puzzled as to why he is just throwing up. All of them have just said it's viral. But it's going on the 5th day of him throwing up everything over half an ounce.. I'm beyond concerned for my son. And I would really like to know what's going on with him