Soy is horrible. I put it up there with cows milk honestly. I am bias though because I am allergic to both.
Have you tried adding a powdered Probiotic to his food? You can buy it in the natural section at most Kroger/Fred Meyer stores. I get the kind that is in the bigger tub..with the yellow lid. I cant think of the name of it right now.
They gave some to my kiddo at the hospital yesterday. He has been having non-stop bum blow outs now since Saturday. Once they got the Probiotics into him, it stopped.
I dont have any other advice on how to get it to ease up. If the doc is thinking he needs to see a gastro specialist, it may be worth the $$ to just get him checked out. You dont want there to be something serious going on and not caught.
Can you apply for state Insurance? The will normally cover any kid that has gone without insurance. You do have to meet certain guidelines $$ wise, but normally they will not turn a kiddo away.