I'm fifteen years old, and when my penis is erect, this lump on the underside of my penis hardens too. I think I was born with this, but the lump is straight in the middle near the bottom, and you can see lines on my penis connecting the lump from my balls to the lump to the head of the penis. Also, it doesn't seem to be a pimple because It's the same skin color as my body. It doesn't hurt to touch. Should I be worried.. What is this?

Well you could get answers on here but you would still be worried. Or you can make an appointment with the doctor and not worry at all. The lines are probably just veins cause veins are kind of important down there. But make an appointment with your doctor so you don't have to worry.