I cannot confirm anything without examination but it can be cold sores or warts. Herpes causing cold sores is most easily transmitted by direct contact with a lesion or the body fluid of an infected individual. Transmission may also occur through skin-to-skin contact during periods of asymptomatic shedding and the virus may sit for many days without any symptom. The third possibility is of impetigo lip which usually begins as a blister on the lip, which may be mistaken for a cold sore.
I suggest you to get it examined from a dermatologist as treatment is different for all. Since it is painful, you can use over the counter topical anesthetics like benzocaine, lidocaine etc. Moisturizer like Vaseline can be applied as it keeps the lesion moist and prevent cracking of the lesion.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.