It's hard to get revved up when you don't feel well. I hope you find an exercise or stretch that can help your back and maybe that will help to motivate you out of the house. Albeit you can exercise in your house by walking around the furniture, doing squats with the kitchen chair and lifting cans of peas. If you were exercising long enough to make progress then it may be easier for you to start again.

I too took carb craving meds that caused weight gain and have been back pain free for a month so I'm trying to get back on the exercise horse and convince myself that even 30 minute mini walks at 3 mph will burn calories (with a sensible diet) and help with muscle atrophy.