If you have been experiencing constant nasal congestion for the past 7 months despite trying different antihistamines without much success, it may be worth consulting with a doctor. It is important to pay attention to any additional symptoms such as fever, discolored nasal discharge, or frontal and dental pain. Your doctor may need to reevaluate your condition and possibly prescribe a nasal cortisone spray if it is indeed related to allergic rhinitis. Don't hesitate to seek medical advice if you have any further questions or concerns.