It's unfortunate, but work has to go on and can't do that with employees that can't be counted on to show up when they're scheduled to.

I would see if you can get creative and find another, additional nurse that can start a 50/50 share with you and is willing to come in when you cannot, at the last moment, and work 100% for the two of you, if necessary. I'm talking about two people working one job, so the 100% would be only one full-time schedule, not two; you would have the priority spot of showing up and/or calling her to show up in your stead if you could not make it that shift.

Or, I would take a leave of absence until I did have the illness under control or could work around it in a reliable manner. I don't think any accommodation laws can work if you are unable to even meet the accommodations.