Suggest Treatment For Head Congestion, Post Nasal Drip And Severe Cough

HAVE SEASONAL ALLERGIES BUT JUST GETTING OVER THE FLU. HAVE HEAD CONGESTION WITH POST NASAL DRIP THAT IS CAUSING A COUGH TO CLEAR THE BACK OF THE THROAT SO VIOLENT THAT ALL MY BACK AND CHEST MUSCLE HURT. SEEMS TO WORSEN IMMEDIATELY AFTER I EAT SOMETHING. HAVE A WHEEZING SOUND IN MY THROAT AT TIMES. HAD MY LUNGS CHECKED AND NURSE STATED THEY WERE CLEAR. SHOULD I BE TAKING SOME KIND OF DECONGESTANTANT OTHER THAN MUCENEX D AND CONCERNED ABOUT THE SEVERITY AFTER EATING.