What Could Cause Blood Blister?

I have a blood blister on the inside of my leg. It's just in fact turned to a blood blister in that dark blood has now filled the area. It's right in the crutch next to my scrotum. Do I pop the blister. Or what cream should I use. This is a recurring blister but the first time it's become bloody. Whoops it just burst been for a shower and put anti bacterial cream on it. Any other advice. In Australia so non prescription medicine available