Is it normal for my skin to do this?

Okay, I've been to the dermatologist periodically to get moles cut off. I had noticed little changes in them, and decided to get a biopsy done on them.

I had one on my arm that I went to get removed. The dermatologist called me and told me more skin was going to have to be removed around that area. He said that when they had examined the skin, they noticed that it had been mutating. I thought I had noticed a change, and I was right. Anyway, he said that the skin had been attacking itself and the mole. And upon further examination, all the other moles I had had removed had the same thing happening to them and the surrounding skin. However, he only made me an appointment to get more skin taken off of my arm and not the other places.

I'm wondering if anybody has any clue as to what could be happening to me. It seems like there's a bigger, underlying problem since what happens to my skin is so strange. It's kinda freaking me out.