I had it really really bad w/ my first. Along w/ PSD. W/ my second I had both bad as well, but went to a chiropractor in the beginning of my last trimester, which is when it gets REALLY bad (you ain't felt nothing yet, you first time moms! Sorry to say!) and while the chiropractor did not get rid of it ocmpletely.. Well, if I had gone twice a week maybe he could have. LOL! But it helped A LOT! W/ both the PSD and the sciatica.
I also found that doing lots of pelvic rocks and squatting really helps to open up the pelvis and feels really good for both of those problems. My chiro also showed dh a pressure point somewhere on my butt cheek :LOL that really relieves it a lot between sessions. Also taking a long brisk walk (no stopping often, so put the kids in a stroller or backpack, even if they hate it lol) also helps to stretch out the pelvic area, which relieves a lot of the pressure feeling.
I bought a prenatal yoga dvd the other day. I haven't opened it yet, but I'm hoping all the stretching will help w/ a lot of this stuff. I really think a lot of this is caused by us being so used to not exercising and stretching enough. Especially if we work, which I did w/ both of my previous pregnancies. Just chasing my toddler around this time is making me feel much healthier and looser than w/ my previous 2. When I was working last time, I found hat if I got up and really stretched (who cares how dumb you look) my whole body at least every hour, I felt much better. I also sat cross legged or w/ one leg up w/ the ankle on my other knee a lot at my desk. That also helped a lot.