Your state of mind affects the little fella. The more you want the least it will cooperate. I found that if I relax and don't think about it it comes (no pun intended) spontaneously. See a urologist. They will usually prescribe you one of those diamond shaped blue pills. But don't depend entirely on them.

You can overload your mind with porn so much that ordinary sexual encounters will not give you the desired Stimulus. Your expectations may be a bit too high and it will affect your "performance". Lay off the porn.