Giving up dairy be hard, but it's doable. If you try it for two weeks to see if there's a difference then maybe it will be easier. You'd only have to try it out, and if you see a difference in your son, you'd have incentive to continue.
Just about every recipe with dairy in it can use a substitute. I use rice milk. There is also almond milk, but if the ped is concerned about nut allergies, I would avoid it. There is also soy, but soy is another common allergen. Hemp milk might be a good choice for some variety. I have a rice milk latte every morning. It does take awhile to get used to some substitutes, but it gets easier with time. Also, your kiddo's health is worth it.
There are a lot of allergen-free recipe cookbooks out there these days. Check your library or bookstore. You can find a lot of info by googling "dairy-free recipes." Ice cream - use sorbet (not sherbet - it has dairy) or rice dream or soy ice cream (if soy is OK for you guys). I have made pumpkin pie using tofu instead of dairy. Gravies and sauces can be made with rice milk.
Going out to eat - order everything with no cheese, no sour cream, etc.
You will need to read labels carefully. Casein and whey are dairy and are usually the culprit in allergies.
QUICK SNACKS - Try hummus with crackers. If you can do soy, you can get dairy-free cream cheese and sour cream that are good. Check the crackers for dairy ingredients, though.
Depending where you live, you may find a store that can help you find some good dairy-free alternatives. Is there a natural foods store that may have more choices than the typical grocery? If not, you can also ask your regular grocery store to stock dairy free items for you. The Safeway close to our house started carrying dairy-free and gluten-free items last year due to demand.
If you go to a potluck, be sure to bring something you can eat. And if you go to a dinner at someone's house, just tell them you cannot have dairy and see if they can accomodate you.
Also, check out vegan recipes. Even if you aren't vegetarian/vegan, they will be dairy free so you can use them or adapt them to your needs.
Good luck.