Hi- I've been having this problem on and off, and went to see an ante natal physio. She said to sleep on your side, with pillows between your legs, then one behind your back, and one under your knees, so you're on a slight angle (not right on your back or right on your side IYSWIM). This did help, although meant that DH was relegated to the spare bed as not enough room in our bed for him, me, bump and pillows! Did it for a week or so, and it did help - have stopped now, and still no recurrence of hip pain.
Also, try to keep your knees together as much as possible (getting in and out of bed, the car, when sitting on the sofa etc) - the pain is caused by inflammation of the pelvic joints - she called it pelvic arthropothy (sp?) - not sure if this is the same as SPD though?), and is made worse when you part your legs too much (isn't that what got us into this position in the first place?? ). I also use a pelvic support belt (actually 2 - one a little thin one, then a big neoprene one over the top - am in NZ, so not sure what is available in the UK). She also got DH pushing trigger points over my iliosacral joint at least once a day, followed by a hot wheat bag to ease off tension in my lower back.
Sorry, bit of a waffle, but hope there's something in there that might help - there's nothing worse than not being able to sleep!