Hi welcome to HCM... Noted you have diagnose with asthma ... It is allergic condition in which patient having hypersensitivity to certain allergen... For confirmation pulmonary function test done... If repeated asthma attack occurs then Metered dose inhaler like long acting salmetrol or formeterol with steroid needed.... As asthma allergic condition itching can occur by histamin when exposed to allergen... Try to identify allergen or do allergy test ad keep exposure to it minimum... Your child also overweight ... Reduce his weight ... As obesity create prolem in breathing... Passive smoking exposure avoided... Onion having antiinflammatory action . So take cooked onion ... Take care.