What Treatments Can Help My Infant With Persistent Cold, Cough, And Nasal Congestion Despite Using Anti-allergy Drops And Nebulization?

my 8 month old son suffering from sold and cough since last one month with runny nose,sneezing, cough,mucus in nostril. he always breath by mouth,nostril almost blocked,weezing sound of whistle while sleeping.......doc says it s upper respiratory cough ....please suggest some med and respules,as he taken anti alargic drops and 3% ns in nebulization but no improvement