What Could Recurring Blood Blister On Lower Back Suggest?

I have a mole on my lower back that acts like a blood blister, it fills with blood and get big and painful but then goes away after a few weeks. then in a couple of months it comes back. It's about the size of a pencil eraser maybe a little larger, it turns red and brown and almost black, looks like old dried blood inside. During the times it's not inflamed it looks like my normal skin color but the skin is a little raised but barely. I know I need to have it looked at and I plan to at my next oncologist appointment but my question is, is that a sign of cancer? I've read a lot of things on skin cancer but haven't seen anything definitavely that says a cancerous mole can become inflamed and then go back down to normal? If it's not indicative of cancer than what on earth would cause this? Or even if it is indicative of cancer, are there any other things that could cause it besides cancer?