Good call OP. Take care of yourself.
My main hobby before the impracticalities of having children was hiking. I love walking and generally being active. When I was recovered from DS2, I took up running and have run several half marathons since. I hate being sedentary, and even times like now with a short term overdose of sitting on family sofas too much gets me twitchy and insomnia.
But walking was out during most of my two pregnancies. The first was the worst as I went veering from permo-nausea that left me barely able to eat and being too exhausted to expend energy on anything other than basic function which finally tailed of around 16-18 weeks and then got promptly replaced by the beginings of SPD. At 18 weeks, I was in London for an event and my legs sort of ground to a halt and I had to keep pausing at every opportunity. By 34 weeks, I tearfully had to accept on the bench by the supermarket checkouts, swigging lucozade and paracetamol before I could face lugging myself back to the car (in a parent space to guarantee that I could access the driver's seat) that even the ruddy supermarket was beyond me. The last few weeks I was stuck in the house unless I could be dropped off door to door as I couldn't get my bump behind the steering wheel, and reach the pedals any more. Because the SPD was unidentified despite going to the GP at 34 weeks, I tried to plough on as long as I could and unknowingly was damaging myself with inappropriate movement while in the swimming pool.
Second time was better. I'd got fit between pregnancies starting from walking 100m to the post box and back and going to bed to revover. The nausea phase was shorter and less intense (maybe helped by better management) and I managed to keep walking and light exercise until 20 ish weeks. When my pelvis ground up on a trip to town at about 25 weeks, I knew what it was and began managing it. I ended up borrowing crutches to keep moving gently within my threshold and kept in better condition. I went through referrals to physio but by the time I'd done all the hoop jumping required to get a pelvic support, I was 37 weeks and could only get through the hospital on the crutches that I'd already acquired! Managing the condition properly helped me retain several weeks of mobility and reduced the pain levels a bit.
When I had a MW appointment at 39+6 and was already beyond the point that I'd reached in my first pregnancy, I decided it was time to go for broke... I took half an hour to slowly lug myself on my crutches down the hill to the appointment about 400m away. I got the bus home. It turned out that the backache that was setting in when I got home was the start of labour and I was holding my baby 10 hours later.
Both my deliveries were difficult due to being back to back. DS1 was an EMCS after a long exhausting labour. DS2 was much quicker. I insisted on being helped with a better position on my hands and knees as actively moving was physically difficult even without the monitoring, but he ended up being forceps in theatre and was nearly a CS. The 3rd degree tear buggered up my pelvis even more and the SPD was slow to go. When DS was 13 weeks, I was still struggling to do that 400m home and ended up seeing an osteopath in desperation which began making a significant improvement at long last.
Why my essay? Because it's a miserable restrictive condition that can have long term consequences and is poorly understood. I recognised what it was because of other people sharing their experiences which enabled me to manage it better second time. It's an under recognised condition that tends to attract patronising, unhelpful comments by people who really don't seem to grasp that SPD stops business as usual and is made far worse by attempting to push through. Working with the limitations of SPD is not lazy, it's damage limitation.