I have a girlfriend and she agreed to have sex with me. At that time I could not get proper erection to penetrate. I was really disappointed by that. I thought the reason could be my everyday masturbation. Can u tell me what real solution is, so that I can enjoy my sex life?

You are developing performance anxiety. Your failure on that day might be because of anxiety. Do not give much importance to that failure. Relax yourself, there is nothing wrong with you.