I don't always give my two penneth on SPD threads, but I think it's important here.
I'm going into my 20th year of severe SPD, sacroiliac joint dysfunction and hip pain. I've had 6 major pelvic operations and am unable to walk unaided. I can't drive and outside the house I use a wheelchair. I was on crutches from 19 weeks and bed bound in a wheelchair from 26 weeks and had DS2 at 37 weeks.
You need to listen to your body and your physio. They have given you the crutches for a reason. You need to take the pressure off your pelvis. Running after a toddler is not an option. I'm a RAF wife, had a 20 month old and no support. DS1 and I lived in my bedroom. We had no choice.
Ice packs and paracetamol are great, but you don't get any prizes for not taking the codeine and believe me, there will be a time when you are desperate for it.
I would look into some sessions with an osteopath or chiropractor. They might or might not be able to help, but it's not a magic cure and your pelvis will still be quite mobile. The belts, and tubi grips, that are sold in Mothercare etc are useless, you need a Serola belt. They are more expensive but they are much better.
Look into buying a long bolster type pillow so you can sleep on your side with it under you bump and between your knees. I bought 2 really good quality ones in the Dunelm sale yesterday, they were £15.99 each. Satin sheets and pyjamas are good because they make it easier to turn in bed. If you don't want satin sheets, a Snoozle is a really good investment. I wouldn't be without mine.
Go up the stairs one step at a time. No pushing pushchairs or supermarket trolleys, definitely no hoovering. You need to do as little as possible. Driving might well become too painful. We you get in the car put your bottom on the seat swing your legs in together. Sit down to put knickers, tights, trousers on. Rest as much as you can.
Think seriously about not going back to work until after the baby is born, honestly. I know the financial side is difficult but you have to think about you and the long term.
Good luck, I know it's not easy.