Burning while urination but gone after drinking water?

I have been experiencing this problem from past 6 months now .just burning while urinating but when i drink water means 2-3 bottles (750 ml) a day then there is nothing no burning i went to urologist and he just say there s nothing it will go away just drink water ... I have done glucose test as well but everything seems to be alryt i dont know what is the reason it causing it any suggestion will be appreciated.