@tjcombo OK, now that one is funny.

The Spanish Flu of 1918 died down during August and nearly went away. But it came back with a vengeance in October, because the weather started getting colder and people started moving back indoors and having large gatherings. COVID isn't flu. But it is a viral epidemic. Don't take unnecessary chances.

@Gendreauj Hetman Black Label?

@SSmith1226 Where is Gort when we really need him?

Pun, n. A form of wit, to which wise men stoop and fools aspire.
— Ambrose Bierce

Try.....

Monster Oil "Original" (Somewhat similar to Hetman #2) or
Monster Oil "Smoother" (Somewhat similar to Hetman #3)

Hetman #2 is my "daily driver", but I have this one particular horn that is only happy with Monster Oil "Smoother". Don't ask me why. I have no idea.

@Dr-GO Dude. Sorry, but that comment is not OK, even if it was lighthearted. There have been times in my life when I made that kind of money and paid those kinds of taxes. (And I'm not an MD.) But there are people on this board who struggle to come up with $100 for a new mouthpiece. I don't make your kind of money today, and I'm lucky enough that I don't need to. But this is a site about trumpet playing. I know the OP was about one of Louis Armstrong's collectible horns, but have a little compassion for the players just trying to get by on gigging.

OK, so thinking about this a little more....

• Mouthpieces are made out of silver-plated brass, gold-plate over silver-plated brass, stainless steel, and plastic (acrylic or Delrin). A small number of craftsmen even make them out of wood.

• If you had a reaction to the "more professional mouthpiece" loaned by your instructor, it might be a reaction to silver or brass (if some silver plating is worn off), or maybe even nickel in stainless steel, if the MP is SS (doubtful).

• If you had a reaction of the (presumably new) gold plated MP obtained by the school it might conceivably be a reaction to gold, but that would be quite rare. Most metal contact allergies tend to develop slowly over time with prolonged and repeated contact.

• If you tested negative for gold allergy, but had an immediate reaction using a new, clean gold-plated mouthpiece, it could be something other than the mouthpiece.

• As suggested above by several people, thoroughly clean, disinfect, and flush everything including all horns and all mouthpieces. Then try using BERP BioOil lubricant, if you are not already using it.

• Then try the gold-plated MP again.

• If that still doesn't work, try one of the ACB acrylic-topped or Delrin-topped mouthpieces mentioned above by flugelgirl.

@tmd He didn't say he's not allergic to silver or brass. (Sorry for the double negative.)

Delrin (plastic) works well for some people with metal allergies, but they're not cheap. Maybe the college knows of a source where you can borrow one to try.

https://store.wedgemouthpiece.com/665mv-trumpet-top-plastic/