For the back, stretching the opposing and adjacent muscles (stomach and hamstrings) might help some. For me, tucking my legs to chest and rocking on my back helps loosen it up some.

Maybe the sternum strap on your pack isn't adjusted well. Generally, it should be just below your collarbone, or lower if this is uncomfortable. Tension it to keep the straps from feeling like they're cutting into your arms on the edge. Also, it sounds like maybe your shoulder straps are just too tight. (just a guess)

I'm a husky guy and weigh around 230, but I prefer to keep my pack weight in the 15-20 pound range for maximum comfort. Other than basic essentials/survival items, eliminate anything which can be shared which your husband is already carrying.

Maybe you could post your gear list, and others could pinpoint items for possible elimination or alternative lighter items?