I am concerned about "_ _ weak personality, you can say some kind of mentle problem also. _ _ ".
 Is your sleep not satisfactory?
 Do you feel lazy and tired the whole day?
 Are you having difficulty concentrating?
 Have you become irritable?
 Are you feeling sad?
 Do you have suicidal ideas?
 Do you prefer to stay alone rather than mix with friends?
If the answers to at least five above questions is 'Yes' you may need some medication.
An important medical fact is that night fall by itself does not cause any weakness or any problem whatsoever. Worrying about nightfall, feeling guilty or frustrated that night fall does not stop can lower your mood and self confidence.
If you are not worrying excessively about nightfall or early discharge than the problem is unlikely to be related to sexual dysfunction
are not uncommon in this age group. Visiting an appropriate doctor for "_ _ _mentle problem _ _" will greatly benefit you.
Do not hesitate to tell your father. He will know the right doctor and will be understanding and helpful. This statement by your father "_ _ but he said that it is a normal problem_ _" is indeed correct.
Let us know the details of the 7 questions asked above.
Dr. Ashok Koparday