I have a hard lump on my forearm just bellow my elbow. its in the middle of my tattoo. what should i do?

Nothing now: Leave it alone unless it gets bigger, red, hot, tender or with other signs of infection., and the you need to see a docto. Might be a local reaction to the tattoo dye and might spontaneously resolve. If is worrisome, the type of doctor to consult with would be a dermatologist.

Concerned: I am concerned for either a skin infection, abscess, or possibly an allergic reaction to the tattoo ink. You need to be evaluated by a physician urgently.