Can allergic rhinitis cause phlegm to irritate your throat & cause white spots on back of throat? & can phlegm discolor your tongue?

No: allergic rhinitis won't cause white spots on the back of your throat or discolor your to tongue, it can cause irritation of your throat from the post nasal drainage , if you have sore throat with the above symptoms better see your doctor, also you might be a mouth breather due to blocked nose, that can lead to discoloration of your tongue, better see your doctor to help you with the cough & insomnia