Dr says my oxy satuation is low-on oxygen concentrator - dr says not sleep apnea- doesn't know why-any idea?

Is your concentration low only when you sleep or also when awake? Did they do a sleep study on you to rule out sleep apnea? If it is only when you sleep, elevating the head of your bed may help. It allows for more expansion of your diaphragm for easier breathing. Could be some kind of respiratory or heart ailment. Could be shallow breathing while sleeping which is different from sleep apnea. Hope they find a diagnosis for you.