Hi Sarah,
Poor you, having a back ache is sooooooooooo horrid, know exactly how you feel. Have you told your m/w yet? If not tell her and ask to be referred for some physio, it'll only get worse as your pregnancy progress's and your bump gets bigger.
You could try a support belt, it may help. I bought one and it just made my bump really hurt but i'm further along than you so that maybe that's why. The only other things I can suggest is taking it easy, not lifting things (esp.heavy things), bend at the knees (hard to do with a bump
) have soaks in the tub with some lavender oil or relaxing bath soak and massages.
Also, at my parent craft class last week, a physio came in to talk to us and told us that when we're preggers we tend to lean back to compensate for the bump or stick out our pelvis, so try and avoid this, also they say try and stop yourself from waddling! and keep your back straight.
Do you have a gym ball? If not, I really recommend getting one (Argos sell them really cheaply) this really helps with bad backs and posture and is good in later stages to help move the babe down into your pelvis ready for labour.
Hope this helps and hope your back improves, but def. tell your m/w about it. My m/w should have referred me ages ago but didn't now i'm really suffering, I got a new m/w now and got my first physio sesh next week.
Take Care.
Nicki.x