My throat has been filled with phlegm all day and now i can't sleep cuz i feel like i can't breathe?

Rhinitis : Do you have any fever or other cold symptoms ? If not , then this may all be due to allergic rhinitis with postnasal drip. You can use an over the counter allergy medication such as Zyrtec or Allegra (fexofenadine) .

Seasonal flu: Stay hydrated, get enough rest and and use OTC decongestants. If it does not resolve in 10-14 days, or it keeps getting worse see your doctor.