Why has my left hand been numb/tingling/pins and needles for almost a week but mostly numb and should i work while this is happening?

You may have carpal tunnel syndrome, but without an examination it is hard to tell. Please see a local physician for an exam and proper diagnosis.

Most likely reason is a nerve compression at wrist, carpal tunnel syndrome. This most often occurs from repetitive flexion/ extension of wrist, from assembly-line work, and keyboarding. Depending upon your work requirements, this could be worsened. Discuss this with HR or your company doctor.