My son has had a dry cough for about 4 months, he had tonsillitis to start with but the cough is still here even after antibiotics. no cough at night.?

He should be seen: It could be pertussis, or cough-variant asthma, even without a night-time cough, or allergy-triggered cough. There are other types of lung problems more common in certain age groups so it is important to know how old he is. No matter what, a prolonged cough is not normal and a complete history including environment, exam, possible blood/skin/xray tests need to be considered.