Hello, i've been popping a pimple type thing on my back for years now. large amounts of the white stuff. starting to itch and bleed a little now.

Uncertain: Don't know if this is a cyst that may have become enlarged or infected. At this point, medical assessment would be your best option to determine what the lesion is and what treatment options are. Take care.

Trichelemmal cyst: These are annoying but not serious. Yours is irritated. OK to continue to squeeze flat. Can be cured by minor surgery.