Why do I have weird fantasies?

So I'm twenty years old. I constantly pretend I'm pregnant but only in the privacy of my own home when I'm alone. I stuff my shirt to make it look like I am and then pretend like I'm being raped. I am aware that it is rather insensitive since rape is such a monstrosity but I somehow become aroused from being the 'victim'. I don't know why I have such the urge to do it for a few days every month. Is it normal for wanting to do this?