Truthfully, I think you need to see your doctor. With complicating factors of your prostate removal post cancer, and long time waiting period of sex with your wife. It's more complex than your normal situation. https://www.hopkinsmedicine.org/health/conditions-and-diseases/prostate-cancer/erectile-dysfunction-after-prostate-cancer The medication is not working for you but there are others to try. There is a psychological component to consider as well. Can you be seen by your doctor to sort this out?