Good news about the stress test and lung x-ray. What you are experiencing could be caused by either sleep
apneaApnea monitor
Apnea of prematurity
Breathing - slowed or stopped
Central sleep apnea
Obstructive sleep apnea
Sleep apnea and/or nocturnal asthma. You could also be having
gastroesophagealGastroesophageal reflux disease
Gastroesophageal reflux in infants refluxGastroesophageal reflux disease
Gastroesophageal reflux in infants
Hiatal hernia repair
Reflux nephropathy
Vesicoureteral reflux (GERD) and that could certainly aggravate any pre-existing asthma. Incidentally untreated sleep apnea can, itself, aggravate nocturnal asthma.
One way to approach this is to see your doctor and obtain a peak-flow meter, a small hand held device that can be used to assess asthma. Then start recording peak-flow values 4 times a day: immediately on awakening in the morning, at noon, at 6:00 PM and at bedtime. If this is nocturnal asthma you may see a significant fall in peak flow overnight; that is, a drop from the flow rate at bedtime to that in the early morning.
So, you should ask your doctor if he/she believes this is asthma, if you have GERD and if, perhaps it might be time to reevaluate your sleep apnea.