I have REALLY bad allergies, and used to be on a prescription nasal spray, like Nasonex until I didn't have insurance coverage, so every allergy season, I'd start taking over-the-counter nasal sprays and would end up to the point where I'd be taking them all the time to help me breathe....
If you've been doing it for long enough, it'll take more than a couple of days to not be congested anymore. My best suggestion is to try the over-the-counter decongestants, like benedryl, for a while, and just suffer... it may take a while, but you will be able to breathe normally again.
I'd advise, that once you are able to breathe again normally, that if your problem stemmed originally from something like allergies, that you go see your doctor, or an allergist, and they can put you on something like nasonex or nasacort that is a steroid and helps open up your nasal passages all the time. don't go back to the over-the-counter stuff though, cause you'll only end up in the same place. if it's a cold, take an oral decongestant, and just suffer for a couple of weeks...