Just checking.... you said, "breastfeeding as much as possible". What happens when it's not possible? Is your son getting anything (formula, etc.) that has dairy? He may have a milk allergy. My dh is allergic to the proteins in milk (casein, whey, and lactose) and if he were to eat 1 piece of cheese, he'd get a headache and be stuffy for a couple days. These ingredients are also hidden in foods that seem to be non-dairy such as cold cuts and baked goods. All you have to do to find out is make sure he's dairy free for a few weeks (no chocolate, ice cream, cheese, yogurt - nothing), then have a "dairy day". Give him a few things all in one day and see what happens. You'll find out quick if he should have dairy!
Let me know and I'll send you a list of the "hidden ingredient" names that are actually dairy so you can spot them on labels. Tom says to tell you he gets a migraine from 1 M&M (milk in them).
Curious, is there any struggle to keep his bowels regular and -ahem- "healthy"?