I've felt a pain above my left eye (a nerve?), and ever since its eyelid has been droopy. an eye md said it could be from the sinuses. could it, or..?

Bell's Palsy?: If the eyelid is droopy and you cannot close or open the eye properly it could be Bell's Palsy. Does your mouth droop on that side? Any numbness? Lyme disease causes Bell's Palsy and should be checked. If the eye is just swollen but muscles are fine then it could be sinusitis.

Yes, maybe: Depends on how "droopy" your eye is. Slight change (not very noticable by others) might occur from sinus infection. Prominent droopy would require tests and could be other. Since you saw ophthalmologist, most likely serious problems have been excluded. If interested, see discussion of ptosis on Wikipedia (for lay-person-friendly discussion).