we noticed it with my ds at around 4 months too. he had a patch of eczema on his back that when we started to put together the signs, we noticed it flaired when i had dairy. itchy eyes and a runny nose. what really made me look into a dairy allergy was what we thought was a yeast rash. we did the 2 weeks of cream and nothing happened. i researched a little, and when i cut out dairy, the eczema went away immediatly, and the rash shortly after.
now hes 18 months, and it shows in his stomach/gut more than in his skin. we thought he had outgrown it at around 9 months, and then noticed that when he/i had dairy, it seriously smelled like something died in his diaper when he pooped. its awful. he also gets really painful and smelly gas.
we're not sure if its an allergy or an intolerance, out ped said they wont test this early, so we just avoid it.