Autism and immunity. To do plz suggesy?

My son has mild autism with sensory issues. Till 6 years old he had runny nose and sleep apnea.now his body not give that much response to dust but for perfume n smoke. I have observed in last one year that due to his low immunity he prescribed many times antihistamine.now his body give weird response to antihistamine if I tell doctor about they took it very casually. My son is not normal n his body also.now a days his fever persist for 4 days ...he required two diff antibiotic dosage when doctor feels first antibiotic dosage is not effective. Now if antihistamine given by doctor he is not able to breath due to dryness or thick phlegm.but I can't discuss with doctor due to fear of insult. But my son really facing issue after histamine.what to do plz suggesy