I'm the opposite of you. I find it much easier to exercise in the morning before an evening shift or even when I get up after a night shift .... than I do after having worked already today (day shift). Mind you, I only work 8 hrs.
Maybe you just need to come up with something abreviated for those days. 20 or 30 minutes of weights, a video tape ... I went for a bike ride yesterday and according to fitday.com it's a much quicker way of using calories than walking.
I used to walk over 3 miles a day but if I work alot, I can't find the over an hour to do that.
The fitness center sounds like a wonderful idea. You'll probably get lots of ideas here.
By the way ... you've done a fabulous job! That's a lot of weight gone