I second your need to go see a physio who specialises in dealing with pregnant women.
i've got SPD and the physio who runs my pregnancy pilates class here in Ballarat is BRILLIANT, she has given me stretches to do, as well as some dos and donts and they have made a HUGE difference. sure it still hurts a bit to walk around, and some days its worse than others, but its not been as bad the last week or so compared to what it was before I saw her about it!
some of the things I've been told that I've found particularly helpful is:
- don't cross ur legs...as much as possible sit with ur knees relaxed and open - like guys do! its much more natural and puts less strain on ur inner thigh muscles/pelvic muscles...so you can cross ur ankles, but dont press ur knees together, let them sit relaxed
- ice your groin...bub gets all active when ya do this lol, but it certainly helps with the pain management
- sleep with a pillow between ur knees on ur side so that ur top leg is flat, not having the knee leaning downwards
- slow down! if you need to turn, turn your foot out to the direction u need to go to and then turn ur body, dont spin around with ur foot still facing forwards
- sit down to get dressed, put on shoes etc, dont stand on one leg to do things like that, it hurts like hell anyway !

hope those ideas help!

oh and as for labour, have also been told on the back is usually the worst position if u have pelvic instability, particularly if u have an epidural bvecause u cant feel if its hurting and can make recovery harder!