Hi--
I went through this with both my children. The usual suspects are dairy products--it is the dairy proteins casein and whey that children struggle with--and gluten products (wheat, barley, rye, and some oats). Rounding out the top seven allergens are tree nuts, peanuts, eggs, soy, and shell fish. It takes 7 days for dairy proteins to get completely out of your body, and therefore your breast milk, so give it some time to see if you get results. Also, be careful--dairy is hidden in everything! You'll have to read labels. If he's struggling with it, even a little bit will throw his little system off. Anything that makes you gassy will make a baby gassy--like beans and broccoli. Also, chocolate is a big one for causing baby gas!
You might also try a few other things. Get your baby a dairy and soy free probiotic (solaray makes a great one for infants) to help get his digestive track functioning well. Also drink mother's milk tea or take the herbs that you find in that tea--marshmallow root, catnip, fennel, ginger, papaya and pineapple enzymes, slippery elm, aloe vera---These will soothe his digestive system and are safe for infants. They will get into your breast milk. They also have tinctures for infants with these herbs that you can give to him directly (just a few drops for a newborn). Check out Wish Garden or Herbs for Kids. If you are willing, take him to a chiropractor for an adjustment of his mid-back and neck especially. If you don't want to go to the chiropractor, you can hold him upside by his ankles and let him gently sway--this is usually enough to align a baby's spine.
As I said previously, both my children are super sensitive and I had to do all sorts of things to get them balanced--including totally changing my diet. It is easier than you think it will be. If I can be of more help, please don't hesitate to ask!
J.