First, you didn't say your doctor was recommending antibiotics for either your gums or your chest cold. GP's try not to overuse anti-b's because of tolerance building up and then germs become resistant in future.
Second, my experience with antibiotics is they did not hurt my UC at all. Except for Ciprofloxacin which is the devil and I'll only take it again if under threat of death otherwise.
Gums: try swishing your mouth out with either mouthwash or (what I would use is
oil of oregano diluted, meaning a couple of drops in 6 ounces of water. Don't swallow, spit it out. Do this swish twice a day.
If your gums stay inflamed in 2 days see a dentist, there may be underlying infection not just irritation.