Get a handtowel wet and microwave it until its warm and put it on your back. It works a little. Not much but its better than nothing at all.
Or take tylenol or alieve.
Try an ice pack n rest..Tylenol can also help
Ice pack will tense the muscles up.. Heat relaxes them.
Icy hot may work
Actually both heat and ice can help depends on the mom's preference.... Research options
http://landmarkptclinics.com/pregnancy-muscle-joint-pains-should-i-use-ice-or-heat/