Do you think the blister on my lip could be contagious? Should I see a dentist?

For about 1 month, I have had a blister of about 2-3 mm on the inside of my upper lip. It doesn't hurt, it doesn't sting, it's not red. Otherwise, my palate stings and I've seen little red spots but my family MD said it was allergies (specifically for my palate, wouldn't say for the blister). My boyfriend and I don't know if it's contagious so we haven't kissed since I noticed. I have no particular health problems and I take an oral contraceptive, vitamin B12 (B12 deficiency has been corrected). However, a few months ago, I started having recurrent vaginitis which was finally diagnosed by a gynecologist as lichen simplex due to excessive scratching (I forgot to tell her about the lesion a/n my mouth). My boyfriend still has lesions a/n his penis diagnosed as balanitis and we had oral sex since (but time of onset of lesion doesn't quite match, it appeared more than a month after oral sex). Stable partner x 1 year, STI tests done, all negative.