The thing that's helped the most re: the fibromyalgia is that my doctor and I finally found a medication that blunts the worst of the aching without making me feel groggy all day (or emptying my wallet). That made it easier to push myself e-v-e-r so slightly now and then without having the usual crash and burn from overexertion. I've probably had FM since about 1980, although it wasn't officially diagnosed till about ten years ago, so there's a long history of slogging along and trying to push the pain into the back of my mind.
I'm trying to decide what to do for a challenge, but even more importantly how to keep the challenge going afterwards and build an actual habit. For starters I may simply log my to-work-and-back walking and add Saturday and Sunday to it. A second possibility is using the challenge environment to correct my ridiculous sleep habits. I think I was born a night owl.