It is difficult to give you a comprehensive answer on this subject but in general terms your sexual organs appear to be working normally. You are capable of achieving an erection and you can ejaculate. Human sexual response can be quite a complex issue and there could be many reasons why you are experiencing your current difficulties. Perhaps it is related to the circumstances during which you and your partner are intimate with each other. Maybe you have consumed alcohol prior to being intimate. Maybe there are issues of guilt involved. I am not ascribing any of these specific issues to you personally but simply trying to outline the diverse range of circumstances that can affect sexual functioning. There are several psychologists who specialise in this area and it would be worthwhile talking to one of them.