In females, increased frequency of urination can be the earliest symptoms of pregnancy. Other than that, it can be due to 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. I suggest you to take opinion of your doctor who would do a clinical examination and advice for needful tests.
I hope it helps. Take care and regards