As Mitzy alludes to, the definition of a masochist is a person that derives sexual gratification from suffering pain or humiliation. There are looser definitions where you don't derive sexual pleasure, but just pleasure in general.
A masochist is one who gets pleasure from being in pain - but is usually associated with sexual pleasure I assume not true in your case, where you cut to reduce feelings of guilt. Please add me, so we can discuss? Mitzy xxx