Mine appeared at about week 20 and I had no idea what it was till I self-diagnosed at about week 32. I had been horse riding, infrequently, till week 28 (separated muscles main reason I stopped - even with the belt it felt like a sack of potatoes hanging onto me by a thin thread).
I did have to use crutches on and off and I would rate the pain during the day at about a 5, and at night having to get up for a wee it was about a 9 - I fell over a couple of times and DP thought I was exaggerating, but my leg just kept giving way under me in the wee hours!
I saw the hospital physio for it and the treatment was pretty useless, but only cost me $10, so no biggie.
I never intended to 'push' in the birth and HypnoBirthing was great to teach me how to 'breathe' the baby out - just awesome. I 'breathed' him out in about 40 or less minutes, I was on my knees with my hands resting on the edge of the bath, and the tub was full, so I had a waterbirth, as planned - DP pouring warm water over my lower back. I'm sure the waterbirth was a major factor in my SPD taking a backseat during labour.
Of course, I also had no intention of using any form of artificial pain relief, so I was quite free to birth in the most comfortable way I felt at the time.
I only noticed the SPD came back about 4 weeks after the birth, and the physio's ended up giving up on it saying that if I didn't wean, there wasn't much they could do.
I got onto the ABA forum and asked around there for breastfeeders with SPD. I was referred to a nearby clinic and they have been wonderful. When I have a set back it's because I have neglected to do my strengthening and stretching exercises, especially before doing something strenuous.
After the birth, when I'm not careful, the pain can get to a 6 or 7, but it's never been quite like the 'sledgehammer up my pelvis' strength that it was in late pregnancy.
Also, I think my core strength has saved me from the worst of it. A combination of horse riding and yoga has kept up my core strength. When I feel it coming on, I immediately adjust how I'm using my legs and hips - getting out of the car and bed carefully, lifting things properly etc.
I recommend a good osteo, and I wore a stretchy band the midwives gave me at the FBC, can't remember the name! I wore it over my belly (separation) and over my hips, but I probably could have done with the belt my SIL kept saying she'd lend me and never ended up doing so!