hi Dreamscaper - welcome!
the things you've described could be symptoms of a lot of things. ocd can bring intrusive thoughts, and you can definitely be dissociative without having more than one personality. there are many possible reasons you might write things down and not remember them. if these things are interfering in your life, and you'd like to get to the bottom of them, the best thing to do is to talk to your therapist or doctor about them.