What Causes Bump On Arm?

I noticed a bump on my arm roughly 6 months ago. I was a little nervous about it so I went to my doctor and had them biopsy it. The biop came back irregular but not cancerous. Now roughly 3 weeks after having it removed it is back. It is a small (size of a pea) red bump located on the outer part of my skin. Doesnt hurt. When it was growing it looked like a wart but now it just looks like a blood filled blister. You cant pop it though. It will just bleed and come back. WTH is this thing? Should I be concerned that the biop wasnt correct? Thanks for any help.