Why does coffee make me sweat?

I’ve been drinking coffee since probably the age of sixteen. I’m twenty-five, now, and I’ve hardly gone a day without a cup. Suddenly, however, I’ve noticed that having just one cup of coffee makes my armpits sweat profusely for hours. I’m puzzled as to how this reaction developed seemingly out of nowhere, as it was never an issue in the past. The only thing I can think of that goes hand-in-hand with this is the fact that I recently lost fifteen pounds.
What is the cause of this? Should I switch to decaf?