Hello and welcome to the subreddit!
Before really digging into your post to answer your questions, I just want to say that your experience is valid and you're looking for answers in the right place. Let's talk about the two things that you are considering: Dysphoria and Fetish.
Dysphoria manifests in a huge range of thoughts, feelings, and behaviors. Everyone's experience of it is different, sometimes in small ways and sometime in very large ways. The bottom line is that there is no invalid experience of dysphoria. In fact, I would recommend that you check out the following web blog via this link:
https://genderdysphoria.fyi/ In this web blog, the author(s) explore the nature of transgender feelings and dysphoria to show the various forms that it can manifest in. Though it is by no means complete, it is definitely the most comprehensive compilation of information on the subject that I have ever seen.
Now to address the idea that "It's just a fetish." I can't even begin to count the number of times I have heard this phrase coming out of folks who were at the beginning of their exploration. Allow me to put this to bed: This idea was coined by transphobes with puritanical leanings in order to try and invalidate the experience of transgender people. Full stop.
Sexuality is part of being human. We have evolved to be obsessed with sex because that's how our species grows and propagates. Any attempt at separation between sexuality and the human experience is artificial and usually perpetuated by people who have puritan beliefs that are used as a method of controlling others through shame.
Now, I'm not scientist, myself, but I'd hazard a guess that the reason why many of us (though not all) end up fantasizing about our parts being different from those we're born with, is that our brains figure out that fantasizing about them during periods of heightened arousal is "safe." In the safe space of our mindscape, we can experiment with how those concepts feel. Those thoughts are, in turn, more arousing because they are affirming; they make us feel whole and complete in ways we may not quite understand at the time.
So! In short: To me, It sounds like what you are describing is your experience of dysphoria. It isn't "just a fetish," because that's not a thing.