What would cause my left hand to feel numb and tingling and slightly swollen?

Number of things: Most common probably carpal tunnel syndrome. However, entrapment of a nerve any where from the neck to the brachial plexus to the elbow to the wrist or anywhere in between can cause these feelings and symptoms. Recommend physical exam to distinguish cause, may need emg.

Possible CT Syndrom: If the hand is swollen then underlying arthritis may be causing pressure on median nerve and symptoms of ct syndrome.