Can extra weight after menopause cause backaches?

Extra weight before or after menopause can cause backaches unrelated to menopause. Think of the body as a balance and when something is added to one side of the balance it creates movement on the other side. When we put on weight particularly when the change is sudden and/or significant there are compensations that have to take place to counter the increased load to our bodies. These compensations take place in the "kinetic chain". The kinetic chain is simply the way our bodies use joints, muscles, and load distribution to deal with gravity. An example of this would be when a woman is pregnant and in her second half of pregnancy her body starts compensating for the load in her tummy by tilting toward the rear to counter balance that load. This is accomplished by contracting muscles in the lower and mid back, rear, etc. This can cause fatigue and pain in the lower back and the stretched tummy will cause temporary dysfunction of the core musculature. This being an example of how increased load can cause lower back pain with no relationship to menopause.

Usually lower back pain is caused by core dysfunction or back pathology (injury) but more frequently core weakness and dysfunction. I would consider menopause generally to be unrelated.