Then go and get the nasal
spray naltrexone, used for heroin overdoses. In the USA you can
buy this without prescription.
Spray it in your nostrils. It blocks endorphins which are similar substances that cause the blood to release from your hard penis. Years ago, when working in a hospital, I can tell you that shooting up with narcan to maintain an erection was quite common. Shhhhh. In those days there was no nasal spray. It has a short half-life though.