1. Insufficient facial muscle flesh mass to cushion the chops against the mouthpiece.
2. Excessive arm pressure relative to the amount you play/practice.
3. Over training. ie putting too much of a physical demand upon your chops relative to your existing condition.
The thicker you cushion the mouthpiece with your chops the less the mouthpiece cuts into your lips/embouchure. Think of your lips as a cushion of rubber against the metal mouthpiece. The thicker you make the rubber the more it shields the load.
You wouldn't drive your car on a flat tire would you? OK so pucker your lips forward a bit and lessen the load. One way of accomplishing this (at least partially) is to pull your mouth corners IN to your eye teeth.
There are other ways of cushioning the mouthpiece load but I would need a diagram to show it. Experiment a bit and have fun.
As far as excessive mouthpiece pressure? This is a variable condition between one trumpet player to the next. When I absolutely have to blow a high, loud phrase and near the end of a four hour gig? I just may jam the horn halfway down my throat to get the note. That said i would never practice this way and only rarely do this in a rehearsal. We can withstand some abuse but not day after day after day. Only through learning the BLOW and keeping arm pressure down to MANAGEABLE levels do our chops grow. Overcoming easily that which once seemed impossible.
Meanwhile listen to Don Ellis until your chops heal. Here
Good Feelin' - YouTube