Possible Ptosis on One Eyelid Appearing Only when Tired?

In 2007 I was checked by an ofthalmologist and he noticed my left eyelid dropping. On 2006 I had lasik surgery (with a few failed attempts at putting the clamps), but I never noticed it before. Most of the day it's difficult to see since I always exercise a bit of strength to keep them raised, but in the moment I relax, it starts to drop and the left eyelid closes before the right one. At the end of day I also feel something inside the eyelid and over the eye, as if the muscle felt really tired.