Get yourself a support belt. You can use it if walking or standing for long time.
You have to alternate between sitting/lying/walking/standing so that you're not doing any of the above for too long.
Only walk for the period of time that is not painful, don't push yourself. Walk slowly, the smaller steps the better. Walking is actually not very good for pelvis, swimming is.
Don't push heavy shopping trolley, pram or buggy. Hoovering is not very good either.
Keep your knees together as much as possible, I.e. When getting out of the car, bath, bed. Don't cross your legs when sitting down. Exercise ball can help - make sure your knees are below your hip level.
Pillow between knees when you're sleeping. If your hips hurt duvet under the sheets can help.
Don't stand on one leg, sit down when you're putting/taking off shoes, socks, trousers, etc.
Don't carry toddler on one hip, or heavy bag in one hand - spread the load between two bags.
Do pelvic floor exercises!
In general avoid any activity that makes you sore.
You have my sympathies, SPD sucks. It will mostly go away as soon as you give birth though.