What Causes Fluid Filled Bumps At The Side Of The Feet?

I've been getting small liquid filled bumps on the side and/or bottom of my feet and I noticed it happens more if I have on shoes but don't lace them up. If I poke or cut them to release the fluid the skin on my feet gets sore after I cut away the skin around the bump. Is this normal and what can be done for treatment. I don't have any insurance.