Hello,
Thanks for posting your query at DoctorSpring.com

I have gone through your question in detail and I can understand what you are going through.
Please try to understand that masturbation is a very natural way of expressing ones own sexual desires and it is very safe and there is no problem associated even with regular masturbation. Secondly there is a continous semen production going on in the body. It will come out either through sex or masturbation. If both of them are not occuring then the semen will come out spontaneously mostly at night. The dimension of penis that you have mentioned is also normal. Moreover its only the outer one third of vagina which is sensitive to stimulus. The rest 2/3rd of vagina is not having any significant stimulatory capacity and hence size of the penis doesnt matter much. A three inch erect penis is sufficient to have a good sex.
When you have sex before marriage there are plenty of doubts in mind and that prevents complete expression of sexual capacity. Mostly you will have a good sex after marriage as you will be having sex with your legally asigned partner with no doubt in mind.
Hope this helps with your concerns.
If you have any further doubts, do let me know.

Kind regards
Dr. Srikanth Reddy MD