Ya, sorry you are having this difficulty. https://www.healthline.com/health/healthy-sex/prone-masturbation#effect-on-sexualfunction I'm sure you've rad all the info on prone position masturbation. It can basically cause a traumatic injury to the penis or nerves. BUT, that typically involves not being able to get erect. You are getting erect but having difficulty with orgasm it sounds like. This can also happen but that is more anxiety related when it does. You know what they say to do, right? Don't use that position, abstain from masturbating altogether for a short while. Try to 'reset'. I also don't know what medication you are on but plenty affect sexual health. I don't see meds for kidney stones on this list though. https://www.mdlinx.com/article/drugs-that-interfere-with-sexual-function/2DX8oKKfmLtyUxNsrSy6kn Checking in with your doctor too would make sense.