Hi, welcome to the forum, the cause of the breathing difficulty should be identified and treated. Firstly it can be an attack of bronchospasm secondary to exposure to allergen. Stinging insects, Aeroallergens (uncommon), Foods and additives like Milk, egg, peanuts, nuts, soy, and wheat are the most common agents to cause generalized allergy . Further exposure should be avoided. It can be in the form of severe asthmatic attack or anaphylactic shock (histamine release).
Also other obstructive disorders should be ruled out such as bronchial abnormality, other conditions like pulmonary embolism, Pneumothorax.
Child may need hospitalization in such cases. Oxygen levels can be monitored by Pulse oximetry, End-tidal carbon dioxide measurement, Transcutaneous CO2 measurement or Arterial blood gas/venous blood gas.
Treatment with bronchodilators with inhaled corticosteroids in the form of nebulization will help. I suggest you to consult pediatrician for further management. Take care and regards.
Sounds like you may need to take your child to the ER. If the breathing is okay now, you should at least call the doctor ASAP and see about switching medications, etc.