There is a vein pulsing right under my left eyelid. i wear contacts. should i do anything?

Likely irritation: This is likely related to surface irritation leading to eyelid twitching. Use some lubricant and limit your contact lens and that should help.

Myokymia: Random twitching of an eyelid, which happens in normal people, is called myokymia (an involuntary, spontaneous, quivering of a few muscle cell bundles within a muscle). Myokymia starts and stops spontaneously. In the eyelids, it can last a few minutes to a few days. It can be caused by stress, dry eyes, lack of sleep. Dryness from contacts.