Hello Heartpony123: You know... I can't say what's going on with you here.

Perhaps a psychologist could offer some sort of psychological theory of what's happening.

Maybe, in some way, it is simply based in some anxiety you are struggling with.
The one thing I do know is that sexual fantasies occur to everyone. (If you continue on here on PC & read various posts, particularly in the Sexual and Gender Issues forum, you'll begin to see this for yourself.) So, from my perspective, while what you are experiencing is obviously troublesome to you, it's really not all that unusual.

And you are most definitely not crazy!
Sometimes, though, in order to get rid of these sorts of concerns, it is necessary to talk them through with someone.

So, if this continues to be a problem for you, my suggestion would be to seek out a counselor, or mental health therapist, with whom you can share what is going on with you. Simply talking it through may well put the problem to rest. But in addition a skilled therapist may be able to help you resolve the anxiety you are feeling with regard to this situation.
Anyway... I see this is your first post here on PC. So... welcome to PsychCentral… from the Skeezyks!

I hope you find the time you spend here to be of benefit.
PsychCentral is a great place to get information as well as support for mental health issues. There are many knowledgeable & caring members here. The more you post, & reply to other members’ posts, the more a part of the community you will become.

Plus there are social groups you can join & chat rooms where you’ll be able to connect with other PC members in real time (once your first 5 posts have been reviewed & approved.) Lots of great stuff! So please keep posting!