How many weeks are you already?
If you are nearing your EDD, then probably it wont go away.
Else, you can try to put some heat pad at your lower back...or try to ask your hubby to massage your back.
And dont sleep on your back or lean 45 degrees on your back (ie: on sofa) cos I realised this will make it worse.
I always sleep on my side with my legs curled a little. And I put a pillow in b/w my legs and it does help...if I feel it's not enuff, I put 2 pillows b/w my legs.
And drink plenty of water cos insufficient water also causes aches. My gynae told me very early - 1st tri.
Hope my tips helps