Gosh poor thing. I really feel for you. Tyler (my 6 month old) was just like that the first 3 months. It was awful. We actually spent 1 night in the hospital because of it. He was in so much pain.
We ended up on Elecare, the amino acid based formula and within a month he was doing so much better.
Now, I don't know if it was just something he grew out of or 1 thing that the GI doctors realized with him was that he had a tight anus.
It is called anal stenosis. He was having a hard time getting even soft liquid poop out and all his gas was backing up and causing pain.
So, I had to do anal stretches 2 times a day to stretch his butt.
Yeah, trust me no fun, but it does not cause them any pain, just relief. You would not believe the gas he would let out.
All I did was get a rubber glove, put KY Jelly on my pinky finger, insert it just to the knuckel and move it side to side.
Before that I would use a Q-tip and just insert it a tiny bit and he would blow out so much gas.
Not telling you to do this, but that was our problem.
Does he seem constipated any?
If the GS does not seem to help, I would cut out all dairy in my diet and really try hard to get him to take Alimentum or Nutramigen.
Sorry you have to go through this. I know it is hard with other kids.