The support group idea sounds good. If you can't find one in your area, perhaps an online support group would be helpful for you. A forum where you can get ongoing interaction, suggestions and moral support from other parents. I don't know these personally, but they look worthwhile checking out: http://community.kidswithfoodallergies.org/forum/main_forum, http://www.allergychat.org/allergy_forum/

And to find an in-person group in your area, this site purports to help find one: https://www.foodallergy.org/support-groups

Over time, you may find it helpful to track some numbers, and there's a nice calculator that gives you percentiles at http://www.infantchart.com/ I put in your numbers and got the 10th percentile.

I wonder if it would be helpful for his doctor to give you a referral to a nutritionist.