Thanks for the query..
The symptoms of post nasal drip
and cough are to infection in the sinuses leading to Sinusitis
and as the sinuses drains through nostrils, therefore fluid/pus accumulation in sinuses can drain through nose..
Coughing is due to irritation and infection in throat caused by post nasal drip..
I would suggest you to consult an Emergency room and get evaluated and a thorough clinical evaluation and investigations like PNS view x ray or MRI scan can help in diagnosis and treatment can be done accordingly..
You can be advised a course of antibiotics, anti-inflammatory painkiller like Ibuprofen, decongestants like Pseudoephadrine, do saline nasal irrigation
, steam inhalation and use a humidifier in your room..
You can also be advised decongestant nasal sprays containing Xylometazoline
Avoid spicy and chilled foods..
Do warm compresses around nostrils..
As you are allergic to antibiotics you should first get an Allergy test done to check for compatible antibiotics and then it can be advised as they needed to be taken to reduce bacterial infection that can continue to cause worsening of the symptoms..
Hope this helps..