Am going to assume that you are young as (obviously) acne tends to hit people of that age more often.
I had a whole ton of acne when i was a pup and many times it occurred in areas on or near where the mouthpiece touched my upper lip. It may have hit near my lower lip connection to m/piece too but the worst ones were always on my top lip. Am an upper lip dominant player.
We've seen a fair amount of advice here all good and yet seemingly contradictory. The problem in addressing the situation is that none of us are MD's and/or none of us can see your problem. So all I can do is tell you what i did/do when these conditions would "pop" up.
Cody is correct to mention to "not pop" it in as much as none of us are medically qualified to pull this off. Now having said that what i did differs with Cody's good caution. Because had i not done what I'm about to tell i did would have missed some very important gigs that people depended upon me to play.
My problem with popping the zit is twofold.
A. Sterility (Cody is wise to be concerned about this)
B. Lancing the thing in such a way as to NOT cause more damage.
SO: My dermatologist cautioned both myself and my sister that if we refused to take his advice and leave the thing alone we should at least:
1. Find a sharp sewing needle.
2. Apply warm, wet and clean face towels to the region for five to ten minutes. Hot as your face can take it.
3. Over the kitchen gas stove or similar open flame heat the tip of a very sharp needle until it (the tip) glows red hot. You might want to wear clean cloth gloves to avoid singed fingers. When cool very lightly penetrate the yellow area. Just enough to allow it BARELY break the skin.
4. Clean with antiseptic as you allow the wound to leak out the pus, apply wound cream and cover with band aid.
You don't 'pop" the area so much as just barely create the smallest and shallowest penetrations through your skin. Why a sewing needle? A sewing needle is the sharpest instrument generally found around the home. Leaves the smallest hole. Other instruments like pins found in mom's pincushion are much too blunt. They leave too large of a hole. Requiring more healing time and leaving the area more open to additional infections.
Again: Everything above probably wouldn't be recommended by the doctor. this is because MD's don't play the trumpet. they don't know the feeling of having twenty members of band class counting on you to play lead and an audience full of families lined up to hear the band play.
"The show must go on".
Having said that? Try not to play very soon after popping the thing. Allow it to heal without playing your horn for a couple days whenever possible. by returning to the horn too quick you may slow the healing process, achieve crappy results from your music and possibly open the god damned thing up again and return to square one with an even worse wound.
Another idea is to prepare in advance for possible future wounds and learn to play with your mouthpiece a little left or right of a hypothetical injury. Then if or when something nasty like this happens you'll at least be able to cover some portion of your parts.
Delegating hard charts to your trumpet playing peers is always wise. Though I'm almost always hired to play the lead book I try to delegate close to half the book to my buddies in the trumpet section. This aids a friendly working environment, creates a "we" mentality and boosts morale drastically.
Just last summer I caught a godawful Kanker sore on my upper lip and couldn't get a note out of the horn for over a week. When the gig came I insisted the cat playing second blow almost the whole lead book. But had I been a pig in earlier rehearsals? He wouldn't have been as prepared to blow first.
Teamwork is the greatest asset you can have within a trumpet section. Always compliment your fellow setion members. Not in a condescending way but with true appreciation.