SPD - Symphysis pubis dysfunction.
I had it with my daughter, and I completely understand how painful it is.
I ended up on crutches for the last few weeks of my pregnancy, but my midwife told me some people get it so bad they end up in wheelchairs! :-/
If I remember correctly, it's where the pelvis bones 'move', or separate. Something like that.
Mine just seemed to come out of nowhere, and night times were the worst.
Phone your local hospital, ask to be put through to the maternity ward and tell them you need a 'maternity belt'. Not the most attractive of things, but seriously who cares, and it kind of 'holds' everything in place and keeps things sturdy. It's a bit like a gurdle.
I feel your pain, it was horrendous when I had it. You shouldn't be working though, I hate to say it, but it gets worse the further along you go.
Get signed off, or take maternity leave earlier than planned.