It happens when bacteria infect the parts of your body that make and store urine, such as your bladder or urethra. Along with seeing blood, you might feel like you have to go all the time, and it could burn when you do. In serious cases, you may have pain in your belly or groin. But sometimes, especially if you’re older, you may not have any symptoms. UTIs are very common, and antibiotics can usually clear them up.