What Causes Right Sided Lower Back Pain?

I have had a back pain now for 2 weeks right where my right kidney is. I asked my PT and he had me touch my toes and bend etc and that is ok. It's mainly when I am sitting that I start hurting. It does come and go and on one occasion, it brought tears to my eyes and a little nausiated just for a short while. I am 63 and active grandma and at first I thought it might be a muscle pull but now I am wondering about kidney stone?!