I Gave My Boyfriend Oral Sex Before Going To Sleep

I gave my boyfriend oral sex before going to sleep and when I woke up my bottom lip was swollen. No itching, no redness, no weird bumps. Nothing it was just swollen not extremely huge but I could feel it. It went down and I ignored it. Next day i gave him oral sex again and it happened again and a little worse than that yesterday. What do you think the problem could be?