Eyelid twitching is actually fairly common, and almost always benign (ie, harmless).
Possible causes include:
1. Fatigue/stress
2. Alcohol/caffeine
3. Eyelid strain
Eyelid twitching often goes away by itself without any treatment at all.
Unfortunately, it can sometimes take a while to resolve completely – as you’ve noted, your eyelid twitching has gone on for more than a month.
Rarely, there are some other underlying causes of persistent eyelid twitching that require a medical doctor’s review. These are often accompanied by other types of symptoms, such as spasms or involuntary movements in other parts of your body.
I wouldn’t be overly worried about your eyelid twitching if I were in your shoes, from the limited amount of information that you’ve provided (single eyelid twitching). However, if it’s a cause of concern for you, do visit a doctor to have him rule out any other possible causes.
If the twitching also begins to affect other parts of your face, or your eyelid starts to droop, do seek formal medical advise sooner as well.
In the mean time, you could try to remove potential causes, such as reducing caffeine/alcohol and fatigue (get more rest now that your exams are done!) You can also try applying a warm towel to your eyelid when the eyelid twitching starts.
Cheers
