Urinary track infection. When 2 drink.

I am suma 30 years old student preparing for Upsc cse.I feel frequent urge to urinate for every 30 to 50 minutes  when I am in reading room which has AC.But only few drops of urine is coming.If I hold urine for extra 15 mts it pains mildly.While sleeping night times I drink 400 ml of water.But till morning 6 to 7 hours I dont feel that urge.Early early morning, I drink 300 ml of water but I dont feel the urge to urinate.It starts 2 hours after i wake up dring day time.I have observed the  the same when I drink 1.5 litres of water a day and 3 litres of water another day.I drink coconut water 250 ml daily sometimes..I have a sedentary lifestyle as a student.I exercise daily.Strictly no caffeine and no spices.It is disturbing my productivity in studies.I am thirsty all the time if I drink less water to avoid urination.If I drink more water at a time also I dont get urine at a time.No medication right now.No burning sensation while passing urine. How much water to drink and when 2 drink.