How many weeks does it take flonase to work with post nasal drip?

Usually it only takes a few days and then you need to consistently use it to continue the effect. There could be a few reasons why it does not seem to be effective - you are not using it properly or you may have a concurrentl sinus infection - both of these are examples of why it may not work so well. Best to make an appointment with your doctor to be assessed and treated appropriately.