A prescription diet will be the best for your baby if he does have liver disease. In the meantime, here is a link that will help you with foods to avoid and foods to help until you figure all of this out. This certainly will not hurt him if it is not a shunt.
http://f1.grp.yahoofs.com/v1/4J8vUBp...ecommendations
Please start feeding him 4-6 small, low protein meals per day. Ask your vet about putting him on lactulose to clear the toxins from his little body...that is what is possibly making him feel bad, lethartic and rub his head - he probably has headaches. His food is making him sick and the toxins are poisoning his little body. If the tests come back that he does not have liver disease, then you've done no harm with this diet - if he improves, great. I'll check back later...