My 2 year old son is having a constant persistent cough but has severe asthma and allergies has moderate to severe asthma and allergies is on an advair inhaler twice a day for the last two weeks and the last three days I switched him back to his Pulmicort

Has . Has he been seen by an allergist, or are these medications being given by his pediatrician.? There may be more going on. Would definitely have him seen by his doctor or whoever is covering for him.
I . I agree with the above answer. He should be seen by an allergist or a pediatric pulmonologist.
Asthma Plan. I would also suggest that he have a CF sweat test if he has not already had this test. Other causes of his cough should be further investigated as well. Every year he should have a flu vaccination, unless otherwise contraindicated. I can review his asthma history while on call Saturday 4-8 pm (Pacific Time).
Poor choice. Advair is not a good choice for 2-y-o child because of unestablished efficacy and of poor delivery of content to young child. Daily use of pulmicort and Albuterol Inhalation as needed via nebulizer would be preferable.