I have a small pimple in the inside of my lower lip, it hurts when I touch it. How can I get rid of it?

Not a pimple. When it happens inside your mouth it is not a pimple. The membranes have various channels where the mucous you make comes to the surface to become your spit. Often these channels become blocked at random from breakage caused by chewing. They can form a small mucus cyst that feels like a pimple. These often need to be cut out to go away. See your dentist or oral surgeon.