Hello. Last night, my lip suddenly swelled - my top lip, on the part that touches the bottom lip. The swelling was localized to around a pea-sized lump, didn t hurt, but seemed to sting and burn a little bit. I put Zovirax on, thinking it could be cold sore , and also put on an anti- histamine . This morning, I woke up, it was gone. What could it be? Is this a cold sore? It doesn t hurt or itch at all. There seems to be some redness on the area. Can you give me some advice as to what to do, or what it could be? I have exams this week, and have been sick a lot recently with winter colds.