This does sounds like a tough case!

Regarding the med where it says you are "expected" to gain weight...can you talk with the doctor about lowering it or replacing it with something else?
On the positive side, you have many good habits already.
No sugar, no flour etc.
I do think the trick is to drink lots of water between meals. If you drink water with your meal, your digestion will not be ideal. Since you are struggling with weight loss, you want your digestion to be ideal.
You might consider using a timer. If I didn't use my timer, I wouldn't remember to drink the water. After a meal, I set the timer and drink two classes. Then I might set if for a half hour and put a little note "drink two more glasses of water". So, then I get in 4 glasses between one meal and the next.
If you stick with very healthy foods only and take a multi vitamin, you can probably stick with 900-950 calories daily. Don't let it go to 1000 until you are more active physically. Perhaps right now 900-950 calories is what you need to lose weight and that extra 50-100 calories keeps your weight on. Something to consider.
Since you are not moving your body much, you likely don't need the usual amount of calories.
It is something to consider.
Also, remember that veggies have lots of water and vitamins...ideal for weight loss and good health.
I agree with Bizi, you might want to ask the doc about physical therapy. Perhaps there is a chance you can get your body in a better place so that you can do a little more physical activity like walking.
I too hope you can feel better, it sounds difficult. Wishing you well.