Do you make him take breaks in the middle of feedings to burp? We have to do that with Matthew (or else the air will get underneath the milk and cause more spit up) and it makes him SO mad that I am taking him away from his milk to burp. He also used to be very hard to burp, though a bit easier now. We do on my chest/shoulder, bouncing him on my knee, leaning him forward sitting up.
Can you hear him sucking in air while he eats? Matthew does this sometimes too even though his latch looks and feels great. Usually I can get him to stop if I hold my boob up or reposition.
I gave him probiotics for about a month and that did help with his gas issues (though not with the spitup). The drops are called Bio Gaia infant probiotics or something like that. They are pretty expensive, found them at Target. And be warned if he spits up any of that, it will leave an oily stain on your clothes.
There is also something called silent reflux, where you can kind of hear the milk come up in their throat but it doesn't actually come out their mouth. Kind of the same sound as if something came up your throat and you swallowed it back down.
Sorry Jack is having troubles.

It's so hard when something is wrong but we don't know what or how to fix it.
Oh and after I came on here and talked about how Matthew was doing better, he had a horrible evening/night. He would not go to sleep and was spitting up and crying again. But he was also running a low grade fever off and on so I'm hoping his troubles were just caused by that and nothing else.