Pain behind the eye with a known history of nasal congestion
and discharge is most likely to be due to sinusitis
. It is very unlikely to be related to any ocular cause. Many a times the sinusitis could be viral ( self limiting), allergic ( responds well to anti-allergy
medicines) or bacterial ( responds well to antibiotics). At this stage it would be very difficult to tell which one of these is the one you have. As you have tried a course of antibiotics already, there is a possibility that the oraganism is resistent to it . Since the secretions have reduced, chances are that you are already recovering from the sinusitis. The pain could be due to some amount of inflammation and congestion of the sinuses
. You can try doing steam inhalation before going to bed every night along with anti allergy medicines suggested by your doctor.
Thank you and best wishes.