A few days ago, I bit my lip incredibly hard. 2 days ago, it was fine but yesterday, it developed into a mouth ulcer/canker sore. It is so annoying and disgusting. It hurt more yesterday, but I still have issues eating. it is located on my bottom lip where the lip touches my top lip. No, it isn't a cold sore - I know the difference. I read that an Antihistamine + Antacid mix helps it. I have no antacid but promethazine is an Antihistamine. Would applying that help? Applying, not ingesting it.