Swelling is a real part of playing trumpet to many players that I have worked with. It is not a problem if you practice enough and have enough command of the face muscles. I would not worry about it. I would practice a lot more soft long tones and lipslurs, soft scales and light articulation every day for 20-30 minutes. After a month or two, you will have built habits that can deal with it. Based on what you have posted, I suspect that you just beat your chops up when playing. Your body is simply fighting back. That is normal. Trumpet playing is not "natural". We have to develop many new habits to play well. Fine motor control of the face muscles, breath control considerably different than everyday breathing, finger/tongue coordination, eye/ear/brain coordination and as in your case, management of irritation caused by pressure on and buzz of the lip tissue. We all go through this. Some of us just don't notice. I think your mouthpiece is fine.