Smaller Penis size and errection problem

Hi Doctor,My penis size is very small,when I get excited its size becomes in between 4-5 inch.Also I don't get proper full errection and whatever partial errection I get,it lasts for very very small time.I want to be very frank about my problem and don't want to hide anything,so I am telling everything frankly. Actually I masturbate alot,I mean almost daily and now I am thinking that, may be masturbation does this to me.Frankly speaking I don't masturbate normally,I mean the way most of the people does. From my childhood while doing masturbation,I lie down on the bed by facing my face towards the bed and rub my penis on the bed.I will be getting married in a couple of months,so I am worried that it will affect my sexual life. I have never smoke,never drank alcohol, never took any tobacco. I even don't drink tea and coffee.Can you Please suggest me any medication or any health tips related to food, exercise or anything related to lifestyle so that I will have normal sex life.Thank you.