What Causes Upper Back Pain,low Bp And High Heart Rate?

my mother had a urinary tract infection...became sectic and was treated at the hospital for 12 days. At home infection came back and was treated with antibiotic. Other symptoms were high heart rate - at the hospital 108 and always quite high. They ran all the tests and nothing came up. Now at home she is having incredible upper back pain, low blood pressure and heart rate is still high. We are not sure how to approach this...doctors say all the tests are normal. They even checked her bladder for tumors to determine if the infection originated from there. any advice?