Its the sleep, I tell ya! It absolutely has to be about water Karin. I would cut out all processed meats (if you haven't already), and when I dropped my diuretic I looked up food sources that act as diuretics...green tea, parsley, veggies. I am actually, currently, not drinking any straight water...I get coffee, a T of ACV in a liter of water (twice a day), and 6 mugs of tea, 3 of which are green. I add parsley or dill (this one acts as a blood thinner) to every protein source. And lots of veggies.
And stress it would be foolish to do any serious exercise right now, with your back, it is not going to keep you from losing weight, especially since you are eating so little right now, so don't stress about it. Plan 10 to 30 minutes for the psychology, reading, listening to meditation, take a nap-lower your stress.