Incessant coughing?

Its seems when my stepfather has a puff on his vape, that's when he coughs, but it never stops, all day and all night. The friggin vape is attached to his hand. But when we went to get our Covid shots, all was quiet...I should mention he's 92, and most people would say...let him be, but when you have to listen to this all night, no sleep! We've been through 2 chest X-Ray, one CT scan. Doctor didn't find anything! I'm at wits end...we've been giving him night time robitussin and coricedin. But 5 hours later (2am) it all starts again..I bought a voice activated recorder to show his doc, but forgot it this morning!