hi silly,
you should probably get this looked at. SORRY!! my dad had something very similar to what you describe. it turned out to be a cyst thing. he didnt get it checked and it got bigger and he had to have surgery. i think it was possibly dangerous because it could disrupt his spine. but im not sure that it was soft like you say yours is. anyways, it might be just a giant blackhead, i have one in my back, not that big though, more like a large pencil eraser top on my lower back. hubby likes to pop it every week! yah, its disgusting, but hes so sweet to me.
im babbling again...bottom line probably get it checked! sry again
clare