I had terrible SPD in my last pregnancy, I was pretty much immobile from 30 weeks, it was awful.
I found that the doctors and physios couldn’t really do much for me, I was advised to avoid any rotation activity (hoov ring/ironing) take stairs one at a time, and avoid weight bearing on one leg, so sit to get dressed etc. Tip for getting in the car is to put bum on seat first then swing legs in keeping knees together, and reverse it for getting out.
The doctors did prescribe me some co-codamol, which I took if I had to leave the house, but I mainly used hot water bottles, tens machine and paracetamol for pain relief.
Good news is that as soon as I’d given birth my spd immediately diminished, and I was pretty much back to normal the following day. It didn’t affect my labour, and there is no risk to the baby. I remember that I was in so much pain I would cry to my husband that I couldn’t cope with being pregnant, and I often thought that the baby wasn’t worth the pain. But he was, of course, and I would do it all again for him. (Begrudgingly)
Get as much support around you now as you can, avoid over exertion, and try to protect your current mobility (by doing as little as possible).
Hopefully for you the pain won’t get any worse, and your baby will come on time.