Talk to Pediatrician on Chest Congestion

My son, who is currently, 1 year nine months old is continously having chest congestion with mild cough for last six months, earlier he had high fever as well, as per doctor he is allergic but food allergen test is negative for all. Doctors have asked to minimize milk and egg intake with following medicines but to no positive effect. Syp. Zatofen Sachet mytica Syp. Acefyl Syp Actified p Please suggest.