I haven't had a chance to read other responses, so this may be totally redundant. I figured out that my ds (now 14 months) had a sensitivity to cow's milk protein. I cut out dairy of my diet and he instantly improved. I never worried about eating things that had been processed on machinery that also processes milk, but I did totally avoid dairy in baked goods til he was a year old. A very good resource is the yahoo group "foodlab". My only advice when you go there is do not bemoan how difficult it will be to cut out dairy. I have been taken aback at some of the responses to that kind of post. The list is really about getting good information about what foods to eat and what to avoid, how to do an elimination diet etc. It would be a good place to ask (or at least search for) about hidden milk protein in foods.
I agree that it is tough to cut out dairy (I do love cheese and milk and especially ice cream), but it is so worth it, and it doesn't have to be forever. I thought it would be so much harder than it was. I have to say, avoiding corn is way harder than dairy. It is in absolutely everything. Another benefit of cutting out dairy is talk about getting rid of baby weight fast! Between no cheese and breastfeeding, it is much easier to get back to prepregnancy weight (if that is an issue for you).
I just looked back at your request and want to add a few things. It took about six weeks of no dairy for things to totally clear, which I think is fairly normal for a person who ate as much dairy as I did. The other complicating factor was that he also has issues with corn and soy, which I didn't eliminate til after I had cut out dairy. Once you eliminate dairy and get to what they call "baseline," a one meal exposure to dairy will clear you and your baby in 4-5 days (in my experience).
I've already written a novel here, but if you want to email, please feel free.
best,
C.
Good luck with this.