Do you mean that your eyeball itself has started to flicker? Have other people said they can see it doing this or is it just the sensation you get?
It could just be that you are not getting enough sleep and tiredness is causing it.
Get yourself booked into the opticians for an eye test,the optician will pick up any problems during the examination.
This 'lid twitch' is very common and usually associated with stress or tiredness. It is rarely associated with any underlying systemic problem but if your symptoms persist then go for an eye examination with your opticiam.
York,we haven't ascertained from DONNA yet whether it is her eyelid or actual eyeball that is flickering...she does state in the original post "not my eyelid" but hasn't as yet confirmed this.