Is this just some light spotting or more than that? Without a uterus, you shouldn't be bleeding. However, vaginal atrophy caused by loss of estrogen can cause some spotting. And I have read situations where some women who have endometriosis can have some bleeding from endo implants on the vaginal cuff. The "feeling weird to pee" and pain in your lower back could be an indication of a urinary tract infection (UTI). You should see your doctor to determine the cause of the bleeding.
Let us know what you find out.