Laura, if you're at all worried, then you should get it checked out. It sounds like it could be a floater (I'm not sure exactly what they are, but I've got one - had it for over 20 years and it's totally harmless, just annoying).
Why don't you phone the optician and explain what's wrong, and see what they say. I'm sure they'll tell you to come in for a check up.
good luck
