I had this problem with my daughter. It was reflux (but I didn't know it at the time). The way acid reflux works is that the valve at the bottom of their esophagus, where it empties into the tummy, won't stay shut.The stomach acids wash up into the esophagus, causing pain.
One way to remedy this (or at least help) is to feed your baby with him sitting up. It is tough, but you can do it. Sit him facing you, with him straddling your thigh. You'll have to support his head. I did this for my kids, and even the one who didn't have reflux, but my let-down was so strong and it helped him not choke on all the milk pouring into his mouth! LOL
Give it a try. You can always do meds. But why not try this first and see if your baby does better without the meds?