Being Overweight, What Could Random Red Blotches On Skin Indicate?

I just turned 51 and am quite overweight. I am getting red blotches that show up on my arms only but they seem to come out of nowhere. Sometimes they look like a streak and other times they are circular. It seems if one appears, a few more appear within days and they take about two weeks to disappear. They are really ugly and I cover them with a bandaid. My mother gets what looks to be the same thing but she usually remembers banging into something before they show up. I am beginning to get really concerned. Any idea what it could be?