Thanks for your comments!
Generally speaking what you describe is somewhat normal. Without masturbating or any other sexual outlet, your body is naturally sexually tense and your body will respond to small levels of stimuli. In fact it will be normal when you have your first sexual encounter to ejaculate almost immediately. If you wait to have sex until you are married, you and your wife should know to expect this. As you have sex on a more ongoing basis, your ability to last longer will naturally increase. It is important for your wife to know this so that she isn’t disappointed if she does not climax the first few times you have sex. Lots of myths and apprehensions get started at the beginning of a marriage only because not enough education about what to expect is afforded. I don’t see anything to be concerned about in what you describe other than your overall anxiety about this subject at large.
I also want to point out that it is normal to have fantasies and sexual thoughts. They don’t need to run your life by any means, but I wouldn’t want you to run into the problem of inappropriate guilt/shame on this topic.
I would encourage you to see an individual therapist that could offer in-depth sexual education and that could help you normalize and accept your sexuality as a whole while at the same time respecting your wishes to wait for sexual intercourse until marriage. If you’ve been diagnosed with OCD then you need to acknowledge that your judgment might be somewhat impaired as to how much guilt should be associated with certain behaviors/thoughts. A trusted therapist would be a good sounding board for you to have.
Please remember that your body and mind being sexual are good, normal things. This is how we have been created by a divine being. Within the context of our religion, we encourage for people to wait until marriage to enjoy sexual activity. However, your body does not know it’s Mormon. Be patient with yourself and understand that sexual response is a normal and healthy part of life – married or not.