(not in your DDC but I was in the July 2010 club, so I was in your shoes last year!)
Just wanted to share that I went through the same thing with my second. With the first, I had some occasional hip, leg, back pain, but it was MUCH worse with the second. Apparently, in addition to sciatica, you may have what is called pelvic girdle pain of pregnancy. More common with subsequent pregnancies, gets worse with subsequent pregnancies, can start as early as the beginning of the second trimester (mine started around 18 weeks), and is due to increased levels of the hormone relaxin that loosens your pelvic joints and makes your pelvis "unstable" (you can google these if you want more info, but that is what I learned). I had all sorts of things done to cope with it, including massage therapy, physiotherapy, orthotic shoes, exercises, pillows, abdominal support belts, and eventually did modified duties at work (I'm an RN, so I went from being on my feet for the whole shift, to doing desk work, which helped immensely). I went off work at 36 weeks, because even the desk work was too much. It was pretty intense, but the good news is that it usually goes away pretty soon after the birth with no lasting effects (mine went away completely around a month after DS was born). Ahh the joys of pregnancy!
It definitely got worse with the passing weeks, and I hope yours doesn't! It put a huge damper on my ability to enjoy the pregnancy, but it was all worth it in the end.