It is possible to develop new allergic triggers. This happens often in patients that may have moved to a new environment. Also, the intensity of the allergy season can vary from year to year.
If your main symptom is nasal congestion or a stuffy nose, it’s helpful to remember that oral antihistamines may be less effective for these symptoms. They are better for itching and sneezing.
It’s possible this isn’t allergic rhinitis (allergies). It could be non-allergic rhinitis.
A visit with a board-certified allergist and allergy testing to discuss the best treatment option would likely be helpful.