Red lump on underside of Penis

I recently discovered a hard, red raised lump on the underside of my penis. It definetly wasn't there yesterday. It is niether itchy or painful. The lump is of an irregular shape, i.e not a perfect circle, and is about 3 millimeters in diameter. It is located on the underside of my shaft and is about 2 centimeters up from the base. It is hard to tocuh and the skin on top feels differet. I cant tell if it has a head (and therefore is most likely a pimple). im tempted to wait a day or two to see if it subsides before seeing a doctor.

[memorys]

no, go to a doctor as soon as possible.you have just perfectly described some form of an sti..... only if its ulcler. because from what i know most spots on the penis are not harmful. only if their painless, and an ulcler are some signs of sti.