Simple UTIs often improve with 3 days of antibiotics and you do not need a urine culture to prove that it is gone. If you have a complicated UTI, you should have a urine culture to show that the UTI is gone. If your symptoms don't go away even with meds, then you may need a longer course of meds, a different drug or different way of taking it.
About 1 in 5 young women who have a UTI will have another. Men are less likely to get a UTI in the first place. But if they get one, they are likely to have another because the bacteria tend to hide inside the prostate.
If you get UTIs often (3 or more per year), then you should see your health care provider. Your health care provider might want to do more tests (such as checking if the bladder empties) to find out why. You may also need an ultrasound or CT scan, which allow your health care provider to look for any abnormalities of the urinary tract. If you keep getting UTIs, a longer course of low-dose antibiotics or taking an antibiotic after sex may help. There are also methods of self-testing that your health care provider may arrange that let you diagnosis and treat your UTIs at home.