5 year old son had IgE 3187 and now 1857 in 2012.He was on asthafen for a year and now allegra (fexofenadine).Frequeltly falls sick with sudden fever and cough?

hyperIGE syndrome . Hyper ige syndrome a primary immunodeficiency needs to excluded. Patients frequently have boils elevated ige and other typical features. http://primaryimmune.org/wp-content/uploads/2011/04/hyper-ige-syndrome.pdf.
Asthma. With a high ige certainly allergy should be suspected but the possibility of a parasitic infection is also in the differential diagnosis. The cough could be an asthma cough and appropriate medication including inhaled steroids may be indicated as a therapeutic trial. If it is asthma then Allegra (fexofenadine) may not do anything for the cough.