Hello, i have sexual problem

Patient: Hello!i am a 19 years old boy and i have a serious problem.my problem is that since i was 14 years old i learned to masturbate, and i did it too much. even 3 to 4 times a day. now i am aware of its harmful effects and i leave it but my sexual and body strength is too weak. i am so afraid of being married, i don’t know that will i be able to make a woman pregnant or not.the other problem is that my penis size is 12 cm.