One swollen tonsil but causing no pain?

i've had a swollen tonsil for around 5 months now, the other one has been fine and have had nothing wrong with it. However the swollen one isn't sore at all and has only enlarged further once and caused pain. any ideas what this could be? i've been thinking about visiting my GP for a while but don't want to waste their time if it's nothing to worry about. Help appreciated! :)