the left hand pinky finger. the joint directly under the fingernail is very swollen. A blister keeps forming between the joint and fingernail. I have poked it and a gel like clear substance comes out. the pressure stops and as it starts to heal it forms again. i was just tested by x-ray and blood work to check for RA. 3 tests done and 2 are negative and one is positive. What is causing this blister as it started around the same time that joint started swelling.