I'd recommend going to your hospital physio - it may not end up helping you, but it's worth a shot. My hosp physio has been very helpful.
I'm nearly 34 weeks and it WILL get worse before it gets better...however, it is supposed to disappear straight after birth. It gets worse because the baby gets heavier and puts more pressure on the pelvis.
The best tip my physio gave me was this: Every movement you make, make it as if you are wearing a mini skirt with no nickers! It works, because like Sammi said, you need to keep your movements evenly weighted over both sides of your pelvis.
Unfortunately, also, if you were planning to use squat positions for labour, maybe think about all fours instead, unless you're using water for the birth (water will take the pressure off the pelvis).
Take small steps, avoid slopes and stairs and try not to pick up anything over 4kgs. Avoid vacuuming, too, if possible, especially if you don't use an upright cleaner. These are just some other tips I was given in a hospital brochure about SPD.
My physio said that the exercises she gave me will help when I brace to make more strenuous movements and that I must remember to do these exercises and to brace, engaging the muscle she's shown me to isolate - this is because the sympyhis ligament is not like an elastic band, in that it doesn't contract when it's been stretched...and you want to stretch it as little as possible!
Just bear in mind that if your physio does any deep tissue work around your glutes (mine were tight from compensating for the instability) it might feel quite painful the next day. This happened to me yesterday - I was almost in tears from the pain, but I had a nap in the arvo and a good night's sleep and today it's back to 'normal'. The deep tissue work just threw things around a bit temporarily.
It never actually used to have a name and there was no idea about treating it in the past. Now it has a name but there's still only so much that can be done about it!
My deepest commiserations that you have this condition Trust us, we know how you feel