I have had some severe migraines. i have been to two neurologists and they have just recommended medications. why would the vein under my eye twitch?

Benign: Most "muscle twitches" involving eyelid are secondary to myokymia, which is a benign flickering, usually associated with eyestrain, fatigue, stress, bright sunshine, etc. But blepharospam may explain your twitch, and, if painful, or increasingly uncomfortable, have your eye specialist evaluate, and treat as appropriate. Doesn't relate to migraine.