Hello. The detail that you have given is not full but yes, it looks like allergy. So, best way to prevent any breathing problem in his case is to remove the source that causes this allergy (allergen). You have to watch carefully,what triggers his breathing trouble and you have to prevent him from getting exposed to it. L-Montus tablet can be given for 4-6 weeks but you cannot continue it blindly as all medicines have some side effect if continued for long. In that case, you need to consult your pediatrician for his examination and advice accordingly.