I have lower back pain & stiffness. but now the bone in my lower back aches. my mom has rheumatoid arthritis. could this be it? or something else?

Possibly: There are multiple potential causes of back pain much more common that rheumatoid arthritis, but having a mother with ra does put you at some increased risk. Don't hesitate to be seen and evaluated.

Possible: But back pain and stiffness is more likely to come from local back minor injury. If you have other joint swellings and stiffness lasting long get evaluated