hello.i understand your condition.
postnasal dripping can be an annoying and uncomfortable situation to be in.
since you have tried some regimens,i would suggest you to follow this for a while and see how it is
-eliminate caffeine from your diet
-drink loads of water,point is staying hydrated and thinning out the mucus secretions that is causing the annoying dripping
-please try newer antihistaminic like
montelukast and levocetrizine combination for 5 days
-Take a medication such as
guaifenesin (Mucinex).
-use
oxymetazoline drops 3 drops each
nostril three times a day followed by vapourised steam inhalation.
-though your xray might seem clear,chances are you have mild infection,
a course of cefixime-
clavulanic acid 200mg twice daily for 5 days will clear it up
these are tried and tested regimens in our clinics and found them effective
.hope it works for you and i have clarified all your doubts.good day