You've developed "rebound congestion."
An OTC nasal decongestant spray can help in a pinch, but you should never rely on one for more than three days in a row, says Bajowala, who is also a fellow of the American Academy of Allergy, Asthma & Immunology (AAAAI). She explains that after repeated use, nasal tissues become accustomed to the decongestant and begin to overcompensate. This causes you to feel even more stuffy than before, and you'll need increasingly higher doses of nasal spray to get relief. If you're already hooked, make an appointment with a doctor who can recommend an anti-inflammatory prescription spray. They build up in the tissues over weeks of use, so they don't provide immediate relief, but they're much safer and more effective in the long run.