It can be due to many reasons which can be physiological or disease-related, and include excessive intake of liquids, diuretic substances (including tea, caffeine, alcohol, certain drugs), anxiety, exposure to cold,
diabetes mellitus,
diabetes insipidus (central or
nephrogenic), urinary tract infections or obstruction, etc to name a few more common ones.
In your case, urinary tract infection should be ruled out by getting a complete urine examination and a urine culture done.
I hope it helps.