if this has been going on for over 3 months then it sounds like something more serious than a cold or sinus infection. could possibly be asthma bronchitis or something else. i would go see an otolaryngologist and ask your doctor's office to refer you to one they would recommend.
my 3 yr old has been coughing over 3 months. been to dr 3 times; antobiotics cough syrup. no sleep. what should i do? . she will be 3 end of december. weighs about 30 pounds. coughs 90% of the day. irritating for her and even those around her. cant go to sleep and when she finally does she wakes up several times during the night. been on 2 antibiotics for sinus infection in past 3-4 months. been through 2 prescription cough syrups as well as 4 otc cough medicines two of which are all natural (honey). also placed on singulair which didnt do anything.