For me, that's a tricky question when is too much exercise.
If I don't get enough aerobic activity, I don't sweat enough and don't get the heart rate going, that is the key, because when I do, good things happen, the endorphins kick in, my sacrum and tailbone start feeling better, as they get warmed up with better blood flow.
This may happen even on days when they are in pain, and if I work through it, they can end up feeling much better
but then other days, I can tell after a few minutes on the elliptical trainer, that it's not going to help, I'm not going to reach that "tipping point" and it's better to stop
(really a bummer when I just downloaded a 24-hour rental movie to watch!)