Hi there
Backpain can often be alleviated by massaging the PSIS's, the bony knobs of the back of the pelvis. These points, about 2" (50mm) beside the lower spine are lymphatic massage points and will help bring in fresh lymph fluid, which supplies nutrients to the lower back muscles. It also takes away the toxins from the lower back to the liver and kidneys.
During the last month of pregnancy massaging these point will help with the release of a hormone called relaxin which will trigger changes in the pelfis to allow birth to occur
This hormone (relaxin) induces a healthy physiological response in blood vessels, increasing dilation and benefiting blood pressure and kidney function.
Make sure to drink plenty of clean unchlorinated water (chlorine is a poison) to allow the kidneys to function properly.
Great to have such a nice partner. Perhaps he could help massaging the points indicated above.
It is great for bonding, and the fetus will be comforted by the warm feeling between the two of you.
Good luck
Kinetico