This is superb advice. Since you are obviously able to get erect, sometimes at inconvenient times and places, you do not have a physiological problem. Almost certainly you are suffering from performance anguish which tends to feed on itself so that the situation becomes ever worse.

As cupar has so wisely recommended, just relax and let nature take its course. I might add that you might want to forget about your penis in a sexual situation. Concentrate on giving your partner pleasure using your hands and fingers and your lips and tongue. If you do this you just might find that Mr Dick comes to life and is ready for action.