Thanks for sharing your concern.
The failure of nebulizer
meds to work goes against the diagnosis of asthma
though can not rule it out.
In view of severe, uncontrollable, violent coughing spells I am suspecting that whooping cough
is one possibility.
Second possibility is unsuspected foreign body aspiration. Peanut / pop corn
/seed / toy part /pen tops etc , could be anything.
Please discuss with your doctor these possibilities so that they can plan relevant tests.
Hope you find the information valuable.