What Causes Pain And Burning Sensation In Penis?

I am an 18 year old male and I m not gonna lie I have been smoking marijuana for 2 years and never had a problem with my penis but recently as of December every time I smoke my penis starts to hurt like a burning sensation then it shrinks in on itself which honestly scares me it hurts when I rub it on my clothes and even if I touch it it hurts I ve been to my doctor and was tested for sexual diseases but he said I might have Herpes but is unconfirmed yet can I get answers here please as to why this feeling occurs ?