white dot under foreskin

I am 18 and have a white dot on the underside of my penis, below the corona. you have to pull the forskin all the way down to reveal it. usualy its small, but when I agitate it (by pokeing it, which is probably unwise.) it becomes sort of tubular and stings. at first I thought it might have been some kind of spot but it hasen't gone away  after some time. I resurched a little on the internet and I dont think its penile papules because there is only one of it, not a row.

kinda freaked out. any Idea what it is?