What Might Be Causing Bumps, Some Nickel Size, On Face?

What might be causing bumps, some nickel size, on face? Not pimple like, no puss. Itchy. They go away after a few days leaving a dry patch that returns to normal in time. No scarring. But troublesome because I've never had breakout problems before. I use makeup and products for sensitive skin and have eliminated spf products. I've had allergy testing in the past that indicated no real problems. This began six months ago when I moved to a high altitude area (from 200 to 6000 feet). Any ideas?