Motivation is something that for me is actually easier since bc. For those very reasons you suggest. I can see and feel the benefits so much more easily than before.
My motivation to exercise before bc was just to loose weight, look better and because I knew it was good for me. That did not tend to work consistently for me and I constantly battled to maintain any sort of routine and let all sorts of things get in the way of regular exercise.
Then I got bc and there were many days during treatment where I felt the absolute worst I have ever felt in my life. I really noticed that exercise helped me to feel better and improved my quality of life during and especially after active treatment.
That was the best motivation of all for me. I just wanted to feel better and exercise was the thing that worked the best for me. I also realised that I had to find things that I enjoyed, not necessarily what was trendy or what others did. For me that was walking somewhere in natural surroundings, using a treadmill on wet weather days and doing a simple Pilates/yoga routine at home.
I have now been consistently exercising everyday for over 2 years since I finished treatment (even Christmas Day, even my birthday, even on holidays, even the day after I had my ovaries removed). Motivation is no longer an issue because I love what I do and can feel and see the benefits. You just need to start doing what works for you.
My life is so much better because I am active. Deanne xxx