I think you child may have cow's milk protein allergy from you have described...did they test for that? My son (11 1/2 mos) has the same. He tried several of the amino acid based formulas like nutramigen, but he refused to drink those. Our solution was for me to go on a dairy free diet (absolutely no cow product, caesin, milkfat, butter, etc.), which is a bit tough because that meant most breads and baked goods were out too. I have to be very diligent about what I eat. By doing this, he is able to tolerate breast milk. Not sure of your specific case, but we had a small allergy panel done at 3 mos old to see if he was sensitive to cow's milk protein, soy, peanut, egg, and wheat. We have tried several of the special medical formulas recent to try and bump up his weight, but he hates them. Out doc does not really believe in putting cereal into any bottles. The rice cereal and fruits (apples, bananas, pears) and veggies (peas, yams, sweet pot) I usually mix with some of the breast milk to get it to the consistency he likes.
As for long term, our allergist says that he may out grow it by 18 most or 24 mos. Apparently may kids do. They will test him again once he is over 12 mos and over 20 lbs. From what we understand, this has nothing to do with being lactose tolerant/intolerant...this is an allergy to the cow milk protein (caesin) and he may be fine with goat milk or sheep milk. In fact I am able to cook with goat milk butter and eat cheese made from sheep or goat, and he still tolerates my breast milk.. I can look up the other special formulas and cereals that they gave us if you are interest... I just don't recall off hand.
Hope this helps...good luck
BTW -- my crazy diet had me shed all my preg weight plus 15 more pounds without any exercise! at least there is a silver lining to it all. I am 3 sizes smaller than before I got pregnant.