Pixie, I feel like I did a very similar thing. Spent the first year with meds that didn’t work, and just doing my daily tasks (like showering and getting to work) was a huge stretch.
Then got better meds but still wasn’t even near “normal” - I was a fit 36 year old before. I only tried to walk 5km on the flat (when I would have easily done 20km as a morning stroll the year before) and was in tears. Then totally unable to do anything for 3 days. Sigh.
Eventually, I accepted that when people on here and in the doctors office were telling me to exercise, what they meant was little bits, starting very slowly. And lots of two steps forward and one step back.
For me I had to change my mindset from fixing a short term problem, to seeing this as training for the rest of my life. When you look at it that way, not getting in condition over six weeks doesn’t seem such a big deal - cause at 36 I was going to (hopefully!) be doing this for another 40 years! It’s a marathon, not a sprint.
It took me two years at the gym with a great personal trainer who was able to flexibly adjust based on how I felt that day, never comparing weights or reps to the week before, but one day at about that two year mark, I suddenly realised I felt good some (not all) days exercising. And it no longer threw out the next two days!
Fast forward another 6 years, and even now, whilst I am in a flare (which as a sideline I’m getting very sick of), I can still take my dog for a 20 min walk each day and go horseriding once a week.
It took 5 years of the tiniest incremental increases in exercise (only increasing when the previous level did not hurt or cause systemic inflammation- that fatigue you get after exercising) to get back to riding horses, but I did.
There is also some really compelling theory on chronic pain that argues strongly against pushing yourself through pain you find distressing- your brain will start to associate activity with distress which is not a good thing.
So, if at 8,500 steps you are highly distressed, you need to plan your walks to LESS than this to start. Start at 5000 (or 2000, or whatever is easy enough to be not unpleasant) and enjoy the sunshine! Keep slowly moving it up in 10% increments till it feels like a little too much, then back off by the last 10%. Then just enjoy that distance until it feels easy again, then increase it by 10%, and onwards. Consistency is the key - if today you feel awful and do less than yesterday, that’s fine, as long as it is something. My goal is always just to actually show up!
Remember, the one advantage of a chronic disease is that we have literally the rest of our lives to get good at managing it. So take it easy on yourself!
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