My face is still slightly numb after 3 days of finishing antibiotics that treated my sinus infection. what could it be?

Not sure.: Neither antibiotics nor sinusitis should really cause numbness in the face. If you are feeling otherwise in good health it is reasonable to wait a few days and see what happens. If it doesn't improve or gets worse you are going to need to see a doctor, preferably a neurologist. If you have other symptoms like blurred vision, headache it would be wise to see a doctor earlier.