Blister on lip

Hello all,

For the first time ever I am getting a single blister like bubble on the bottom of my lower lip. The first time it appeared I played with it and it got bigger and then I popped it. It came back about a week later in the same exact spot. This time I left alone and it popped overnight on it own.
This morning it looks like its coming back on its own.
Ive read that this is most likely nothing significant but I worry because my lymph nodes in my neck have been bothering me. Every time I work out, I feel sick - sore throat, increased phlegm, stuffy nose.
Any thoughts? How worried should I be?
-Thanks