I don't think it is anything to worry about. I have 1 pretty much in the same spot and it isn't something that is very concerning for me. I think it is some type of gland (maybe a gland that produces the alkaline for masturbating.
I have i believe one small lump on my shaft, near the head of my penis, and i've had it for a while, i don't plan on moving it, but i've had a psyichal every year, i've been so far classified as fine.
Maybe you should look it up?
IM NOT SURE WHAT U HAVE BUT THAT HAPPENS TO ME WHEN I MASTERBATE BUT I ONLY GET 2 LUMPS