Suggest Remedy For Skin Rashes And Small Dark Bruises On Torso

I'm 54 years old, 5'' 3" and about 115 lbs. No medications. I've been getting a lot of skin rashes on my torso lately, which are agrrevated by sweat when I work out but then this week, I found that I now have small dark bruises on the right side of my torso, just below the rib cage. There's no cause for them that I'm aware of (i.e. I haven't bumped into anything, haven't been hit) and there isn't any pain associated with them. I've had them for about 5 days now and they're not lightening up at all. Any idea what the cause might be?