I did for quite awhile after having pneumonia

Yes I have used it while being on oxygen though I don't have to use it much

Sure. Using 02 ensures that your body gets the 02 it needs to make everything work the way it's supposed to. It doesn't do anything to "fix" your lungs, so you still need to take all medications and inhalers prescribed, including your rescue inhaler when you need it.

Yes I am on oxygen and have used the inhaler

YES!!!!!