Laying on my back a lot.

Lately my back has been killing me and the only thing that helps is if I lay on my back. I'm 24 weeks and have read that laying/sleeping on your back isn't the best thing because it can cut off certain circulation.

Is it really that much of a bad thing to be on your back? My bump is still pretty small and (I've gained about 13lbs so far) so I'm hoping it's fine at this point. I'd love any opinions. I'll ask my Doc at my next appointment on Monday too of course.