After uti treatment my urine culture is now finally negative, no infection but i still have symptom of burning in urethra. what can be cause? thanks!

Give It More Time: While the infection is gone it may be that there is still the need to heal completely. And there are a lot of factors specific to you that may play a role (activities, sitting, diet, medications, etc etc etc). So if there is still pain after a few weeks you should discuss this with your doctor. There's something called the 'urethral syndrome' that could be a model for what you may have developed..