I wondered what you do for you work but what ever it is after reading your posts I think it is time to start looking for a new job. Life is too short to be working like that . I sure hope your pay is fantastic.
I teach grade 3 and it is very demanding. I am on my feet all day and at night it is a real effort to go out and walk. Forget the gym. However how about a treadmilll in front of the TV.
Or set the timer and go like a maniac cleaning one room for 15 or 20 minutes . Now there is some fruitful exercise.
Start out with baby steps and walk at lunch for 10 to 15 minutes.
Keep in touch and let us know how you are doing.
Norma