I've had a couple of bouts of backpain this pregnancy, but I've also had it when I wasn't pregnant, I'm not sure it's any different, it just hurts!! The thing I found that helps is not staying in a position for too long. Even though it's kind of uncomfortable to get up and down, just staying sitting doesn't seem to be a good idea in the long run for me. So I would go for a gentle walk, then lie down for a while, then get up, make a snack, then sit, iykwim, just to make sure I wasn't sort of seizing up.

Heat packs helped numb the pain. A painkiller will help you relax a bit so that your muscles can heal themselves - if you are in pain all the time then your body won't be able to heal, and it's exhausting. If you can afford to go to a physio s/he might be able to give you some gentle exercises.

Hope you start to feel better soon!