Recurring blood blisters on stretch marks

I am a 22 year old caucasian woman, good overall health, and a mother of a two year old little boy. I gained alot of weight rapidly while i was pregnant so, of course, I ended up with what looks like a road map of stretch marks in various places. My upper thighs are littered with them and every once in a while I get these blood blisters directly on a stretch mark. They are not restricted to just my thighs although I get them there the most. I've gotten a few on my breasts, a couple on my lower back, and one on the back of my leg. They are painful to the touch, can get fairly large, and stay around for weeks. No matter what I do, whether I leave them alone and let them heal, or pop them myself they leave horrible scars on an already ugly stretch mark. What are they, whats causing them, and is there anything I can do to be rid of them!?