hi, 

few day back, I observed a small bulb kind of think on the shaft of my penis. It is 1 centimeter below the head of my penis foreskin. after some observation my I found it is on a vein, and during erection it also grow little bigger. It round, no pain. I can remember, it is there since many years but was very small (tough to observe easily) but now it is 2-3 millimeter of radius. please suggest me what should.