I can relate, although my obsessions seem to last longer than a few days. They also seem to cycle through. I've had the serial killer one (honestly it's the one I struggle with the most often. It's the most terrifying to me), feared being a pedo, feared being schizo, and the shortest lasting one was when I worried I was "becoming gay" for a few days. All this since september/October.
I guess we worry about becoming the things that are the opposite of who we are. It seems like some people have a single obsession day in/ day out, others cycle through them. Either way it's terrible.
We could all use some kind words of encouragement now and again! Just know that you're not alone on the ever-changing obsessions!
Best of luck!