Perhaps a belly bra would help. You can get them from Babies Galore, DJ's and other baby stores. Its just an elastic band that goes around you. I know its hot this time of year but I did notice it helped on days when it just wouldn't back off.
My back pain was higher as I ended up with 3 dislocated ribs from everything growing and to be honest that was the worst of my symptoms on this pregnancy. It lasted ages and only stopped about a month ago I guess when bump dropped.
Heat bags and a back adjustment regularly probably wont hurt either. I have been seeing a Chiro for many years and just had my last appointment before the big event last week and it made a huge difference. I used to go once a month.