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The main causes which can cause increased frequency of micturition are:
Diabetes mellitus: due to an increase in sugar in the blood, this can cause increased frequency of urination.
Diabetes Insipidus. In this, the brain stops producing a hormone called ADH. The kidneys then produce an excess of urine, this in turn makes the person drink more water, and it becomes a cycle. This form of diabetes insipidus is called Central Diabetes Insipidus. Another form called nephrogenic DI is a hereditary form in which the symptoms are present from childhood and where the kidneys fail to react to ADH which is produced normally from the brain. Link
Prostate problems: Hypertrophy of the prostate or any abnormality can cause this. You need to be investigated for this with ultrasound and clinical examination.
Psychological: Psychological causes, habit forming like tics, can also cause this. This is called Psychogenic Diabetes Insipidus. This is a condition when a person gets into a cycle where he or she feels constantly in need of water and drinks lots of water which in turn causes excessive urination. This is easily distinguished from true diabetes insipidus by testing.
I would suggest that you approach a urologist. You need thorough investigation. The test that is important for you is Voiding Cystography, you can discuss this with your urologist. You should also do the investigations for diabetes mellitius and insipidus. I hope this answer was helpful. If you need more information, feel free to ask. For accepting this answer, please click on the green 'accept' button below. Feedback/Bonus will be warmly appreciated.