My hand keeps going numb. when i'm writing or even when my elbow is just bent. it's occurring more often. what could it be?

Ulnar Neuropathy: Ulnar nerve irritation may cause the symptoms described. Causes include: sleeping with the arm folded behind neck with elbows bent, resting the elbows on the chair arms while typing, resting or bracing the elbow on the arm rest of a vehicle, bench pressing, intense exercising and strain involving the elbow, holding a cell phone to the ear for prolonged periods, using mouse on a hard surface.

See details: Depending on the fingers involved, the two most likely causes are carpal tunnel or cubital tunnel syndrome. Have it evaluated.