What is this thing on the inside of my lip?!?

For the past four months...off and on I'll get this little clear bubble on the inside of my lip. Its like it fills with liquid till it pops on its on...then stead of runny water based stuff...this thick slime comes out...its clear no odor, or color to it at all. Nor flavor. I can't afford to go to a oral Phys. Any suggestions as to what this is or how it got there?