I have recently noticed a hardened vein on my penis which can be felt just under the skin

I have recently noticed a hardened vein on my penis which can be felt just under the skin.?
I have recently noticed a hardened vein on my penis which can be felt just under the skin. It runs along the top of the shaft down to the base. the vein seems to be getting harder/ longer. It is not painful but it is more noticeable when I have an erection even while limp the hardened vein can be felt beneath the surface.I currently have no problem getting an erection. However when I have an erection I have noticed that all of the veins on my penis are now more prominent.
i am a 23 year old from u s. I am not sexually active on a regular basis, other than masturbation. I am not circumcised and I am not taking any prescribed medication. I have not yet discussed this problem with a doctor. I am naturally concerned about this problem. Any advise would be very much appreciated. Thanks for your time.