What Causes Painful Red Blisters On Abdomen?

I have about seven blisters on the right side of my abdomen. They came up in the last couple of weeks. They are red in color with a small knot under the skin like a tiny pimple, but painful to touch. They did not come up at the same time. They are very warm , almost hot. At first, it felt like a small boil. Just don t know. One popped up on my right breast, and today another pimple arose on my the inner arm just below the elbow, about two inches below the inside bend of the elbow.