It could be a urinary tract infection along with a kidney infection. But usually a kidney infection will hurt on both sides a little lower on your back.The only way to find out for sure what's going on is to see your Dr.
if there is a slight trace of blood it could be kidney stones, when i have kidney stones its usually my lower back that hurts. you could have a uti
Could be a urine infection or pelvic infection. Do you have a fever...
Could also be cystitis, which is a common complaint with females. symptoms are burning pain when urinating, and frequent urinating, with very little urine be passed. Talk to a pharmacist or your doctor.
Hope this helps.