What Causes Blood Filled Bumps On Buttocks, Thighs And Legs?

Ive been having these blood filled bumps that pop up from time to time usually on my buttox in the same few places, but also sometimes at the very top of my inner thighs at the crease of my legs. I have no idea what they are and they are incredibly embarrassing. What are they, and how to i make them go away?