Hi there confused. I'm a woman, so I can't relate to erections, but I can relate to the groinal response. When I had images in my head, they were to do with me fondling and committing oral on little girls. Why? Because my fetish is to receive oral and to be fingered, therefore I got very intense arousal to these images. I think OCD combines something you love with something you hate. Now, the images come a couple of times a day, but I don't get aroused. I spent a whole week on this site, talking, researching, analyzing and testing myself. In the end, I said Out Loud to myself "I'm a pedophile." Then I looked at a picture of myself (because I can't look in the mirror right now) and I said "You are a pedophile" and immediately burst into tears. It was then that I realized that perhaps this is all just in my head, because, 1) a pedophile knows what they are at age 14, 2) you can't just suddenly turn into a peadophile, 3) I studied 16 hour days at times, cried, and literally went into a breakdown when a paraphillia from this site told me "it's not the end of the world to get aroused by children." I'm pretty sure a real peado would just accept who they are, and would download CP anyway, and would get off to the images in their head, and surround themselves with kids at any given opportunity.
Sorry for throwing in my story, but as each day passes, the thoughts and worries are slowly gliding out of my head. The images are still on and off, but I don't get aroused any longer and that has solved a lot of the problems for me. You've gotta just let the images and thoughts float in your mind, and try and carry on with normal life if you can. It took me about a week to adjust, but now I'm functioning again, eating again, and laughing again. They say stop testing yourself, but I continued to test myself. Now I don't need to anymore because I've blown off enough steam.
So no you're not the only one who gets the groinal response. I put an image in my mind of my boyfriend, and tested between real arousal and fake arousal. The arousal I got for him was throughout my entire body and I felt comfortable with this arousal. Maybe find something that makes you truly aroused, a memory of a girlfriend or something, or the first time you had sex, or even put a scenario of having sex with someone in your mind, someone you really want to have sex with, whether it's your wife or girlfriend, picture them in a really hot scenario. It worked for me anyway.