What Causes Spotting And Lower Back Pain Post Menopause And Hysterectomy?

I am post menopausal 7 yrs. hysterectomy. For the past 2 years an and off, have had vaginal bleeding. spotting, no great amount. Wear a pad. At end of the day I can tell its been blood. Sort of like the end of a period color. Not bright red. Have low back pain, but i attribute that to back problems i have had for years. Deg, disc dx. arthritis. etc. I have no urinary complaints, so not a uti. I know those symptoms. Not sexually active for over a year. Saw a gyne md last summer said nothing wrong. I am wondering if it could be bladder? No blood in urine. So why is this happening and what is it?