UTI pain does subside as the bacterial infection is killed off through antibiotic treatment. Antibiotics are very effective in treating UTIs and work rather quickly for the types of bacteria that begin spreading in the bladder where urine is building up between trips to the restroom. As soon as this process begins the pain and irritation that accompany UTIs begins to subside until you are completely pain free.
Even though the antibiotics begin reducing the irritation there are still some side effects of the UTI present, like the inflammation of the bladder walls, which take longer to subside. This inflammation is what results in the burning sensation felt while urinating, and this specific form of UTI pain takes the longest to go away.
If any UTI pain persists for more than a week while on medication a doctor should be consulted.