The rule of thumb is that we don't rush to the doctor with something that has been there less than a couple to three weeks. Most irritations, small ulcers, herpes simplex, and marks from trauma go away in somewhere between 14 and 21 days. Of course for those in the middle of complex treatments after diagnosis things are different. But for most American's this rule is appropriate. Things that are persistent we worry about. Persistence is over two weeks for sure. Given your recent illness this could all just be related to that. I'd give it a little longer to resolve and then go see an ent or dental professional about it. Of course under your tongue on the floor of your mouth it is the most colorful part of your oral soft tissues naturally, given the high level of vascularization there.