I am a fellow HOCD sufferer and I have dealt with this during sex. "You want to stop. do you really like this" It is pretty clear it is just a trick but u just have to accept it and move on. Say back to it, "yeah i probably hate this" and keep going. that is the only way. and eventually with time it will go away. Im also 18 so trust me we are in the same boat and youre not alone.