For me the pain started in my coccyx, technically I have sacroiliac pain too but it's basically just the whole pelvis being unstable. I think the term SPD is used commonly as a substitute for what is actually 'pelvic girdle pain', just meaning that it's not just the pubic joint at the front that is unstable. I have pain in my groin and when it's bad it radiates down into my thigh too. I first raised it with my MW when she was trying to check for bubs heart beat and I said I found it so painful to lie on my back (the sacroiliac pain primarily) but then as she measured the fundal height my pubic bone was very tender. If I'm on my feet the pubic bone starts to really ache. At best it feels like I've done three days straight at the gym, like you need a real good stretch and you've found muscles you didn't know you'd had, but doing that stretch just hurts even more in the longer term.
When I get up to stand my pelvis clicks, and I can feel it grinding when I'm walking. The tubigrip actually feels like it's holding your pelvis together, and because it goes right up over your bump too it helps to take the weight of the baby off the pelvis a bit too. The phsyio did advise to sit on a gym ball for 30 minutes each day to tone the core muscles but I've not noticed any difference from this. Also to avoid things that involves spreading your legs, so getting in/out of a car with knees together (much easier if you put a bag for life under you on the seat to reduce the friction), breast stroke is bad, any straddling or true squatting.
I don't think I'm very good at describing it at all,
Hope this helps!
