Sexual tendecy for backpacks?

I am asexual and I am a 18 year old male high school student (senior year) but for some reason I have a tendency to hump any backpack I own, or sometimes just wanting to hump it. Though i've never actually humped a backpack, but I do sometimes do small pelvic thrusts against it so that no one can tell that i'm humping it. I usually keep my dong in my pants when I hump my backpack but, I have temptations to hump it with my dong out. When I say "Hump it with my dong out." I mean actually hump it, not just little pelvic thrusts... but of course if I hump it with my dong out, it will be in private. I think I have a backpack fetish. I'm not sure how or when I devoloped it, but i did. .-.