flesh coloured bumps/spots on shaft of penis

I am concerned about a SINGLE large lump located on the bottom back side of my penis. This is a plain observation of what i see it to be. Large - Size of a pea which includes width and hight. pale white coloration with small amounts of red irritation surrounding it. Its smooth and has a indentation on the top like it was pricked with a needle. I had the same thing pretty much in the same spot 5 months ago. I did go in for testing but it turned out to be nothing. It is some what irritated, it hurt's a little but maybe because i tried popping it. I know I know don't pop it but its a quick way to figure out if its a pimple. Also as a note the last time this occurred i was sexually active. Now after 5 months and sexually active again the same pump re-apeared. Coincidence ?? The fear is STI's any professional opinion's.