This is Dr. David
you need to have a urine culture to find out what bacteria is growing in your urine
a urinalysis is not enough to tell for sure if you have a UTI.
some bacteria in the urine can be resistant to certain antibiotics.
if you drink alcohol or caffeine and don't drink enough water, this can cause burning with urination which can feel like a UTI.
urinary frequency and lower back pain can be from you passing a small kidney stone going down your ureter into your bladder.
you need an ultrasound or CT scan to look for a kidney stone.
vaginal bleeding would causing bleeding all the time, not just when you are straining with bowel movements.
at your age, are you still having your monthly cycle?
when was your last gyn exam?
I bet the bleeding is not due to uterine cancer. you should get a gyn exam and uterine ultrasound.
ask for a urine culture and check for kidney stones.
let me know if you have questiosn.