I can understand your concern. Let me tell you that 4 inch of penis size when erect is normal. You must look to follow healthy sexual hygiene in order to have good erections. About premature ejaculation problem. There are many factors to consider before deciding the management. Factors such as anxiety, stress, masturbation habit, etc, these needs to be taken into consideration for management. With suitable medications and instructions the time to ejaculation can be prolonged.