Shortness of Breath. Such an issue?

This issue started in August my 2 year plus kid suddenly has fast breath/shortness of breath like sound. After that we got Chest X Ray, CECT Chest, Laryngoscopy done. All came normal. Then we took him to the Child Chest Specialist in BLK-Max Hospital. They have suggested for bronchoscopy, we also get that done it also came normal. He has suggested Budecort Inhaler and Metatop Nasal Spray for 15 days which are steroids. We have given it for a few days. But this issue is recurrent. Sometimes these sounds don't come for many hours and sometimes these sounds come 4-5 times in 30 mins. No idea which doctor to consult. There is no issue while sleeping but he has a long sigh during sleep sometimes. Can anyone come across such an issue? We are too worried.