after rereading your post, it could be OCD... when you say that sometimes, you are fine and the thoughts don't even come, that made me take notice. see the thing with OCD is that it can come and go in a heartbeat. One day it will be so triggering, and the next day, it will switch on you into a new obsession. I would watch for that...

but what you are describing also sounds like paranoia to me. Or generalized anxiety. Again, as before, seeing a psychologist is based on how much it is affecting your everyday life. But it wouldn't hurt to get checked out anyway, if not to dx you, then to rule out posible disorders... best of luck!