P.W.
All I can do is reiterate that in time it will pass. I remember feeling EXACTLY the same way that you are -- and my youngest wouldn't let me go to the gym for the exact same reason. I thought I would go insane, and I remember crying one day I was so frustrated.
However, time does pass, and you get through it. I suggest you find something you can do at home. I stopped going to the gym for years for other reasons -- no gym nearby and no money for it anyway -- and learned to work out at home. A jumprope is great exercise, and you can do it with your kid right there. 3,000 skips takes about 1/2 hour, and is great for arms, legs and abs, and will leave you red and sweaty. Maybe not as fun as the community of the gym, but it's a workout.