What Causes My Right Eye To Feel Droopy In Morning?

Hi, My right eye sometimes feels droopy in the morning. It is not exactly puffy, but my eyelid feels heavy, like it is still sleepy. And also when I get tired toward the end of the day, it is always my right eye that seems to want to close. I have had sinus issues in the past, and frequently get the classic sinus headache above my eyes and in my forhead. Could this be cause by inflammation in my sinuses, even if I have no congestion? I have had several eye tests by my opthamologist to make sure that there was no pressure behind my eye or in that area. Any ideas? I am 53, 4'11" and 93 lbs. I am also very active and healthy.