What Causes Blood Blisters On Chest?

My 10 week old baby has blood blisters that have been popping up since awhile. The main one is on her chest, near her heart and grows regularly. Started at pin-prick size and is now an over-grown pea within about 2 weeks time. The other ones are little and on limbs. There is one under her eye but it seems to be going away. Is it something to be worried about?