Hi, it also sounds like something I had going on a few years ago. It turned out to be the begining of tendonitis. My chiro figured it out. Are you doing anything that is repetitive using that hand? Mine was from cleaning horse stalls and shaking out the "good" shavings. I wore a brace ONLY when I was in the barn and it went away.
Like the others said, if it gets worse or is really worrying you call the doc sooner. Good Luck