While on an antibiotic for a uti how long will the frequency and burning still persist?

It depends: Typically, symptoms from a UTI will resolve within 1-3 days after starting appropriate antibiotic treatment. If your symptoms are not improving after this timeframe, or seem to be getting worse, you should go back to your doctor because you may need a different antibiotic, or you may have a condition other than a UTI that needs to be diagnosed. Hope this helps!