Always during the beginning of my menstrual cycle, I get a blood blister (very close to the surface of the skin) on the right side of my stomach. It is painful, rather small (the size of the end of a pencil eraser), and comes to a head. I know I should not, but sometimes to relieve the pain, I pop it. The blister itself bleeds first, very thick and dark blood until the blister is flat, but still present. Then, clear liquid comes out of a tiny hole NEXT TO the blood blister. This is odd and I do not understand why there would be two tiny holes. Is this a boil or a pimple or what is it? Why do I get these ONLY during my period and no other time?