Loss of sensation on penis and numbness.

1.) I do not feel any sexual pleasure on penis or its shaft when it is  inserted in vigina. I mean i heard people saying it feels good but i have not felt such good sensation. and sometime penis lose erection inside vigina. I tried 'tazzel 10 mg' which helped in maintaining erection but that also delays ejaculation for very long time making sex discomfortable for me and my wife. And erection remains for long hours causing pain. 2.) I also feel either my penis is thin or my wife vigina is not tight enough for sexual pleasure so i prefer masturbation over actual sex for pleasure. 3.) If i stop stroking penis, it lose erection rapidly. 4.) Also, while having sexual intercourse, while stroking, my pines becomes numb and i have to stop stroking to get rid of numbness and coldness of penis shaft.