It could be worts & worts are a viral infection. I would call your doctor or even a dermatologist to see if that is what it is. I have had them on & off all throughout my life & that's what it seems to me. They can have one bump or several bumps or clusters of bumps. They just come out of the blue & I am told that something triggers them (ie: stress). I hope its something simple for you. Best of luck.