Hey - not sure whether you'll see this reply (being as it's a while since you posted), but I can really relate to what you've posted about obsessive thinking. I've struggled with obsessive/intrusive thoughts for many years (since childhood, really), often taking the form of very vivid imagery. Similarly, I share your difficulty with over-analysing things - particularly as regards social situations, which I can spend hours 'unpicking' in my head afterwards to try and reassure myself I haven't done anything wrong. A few years ago, I was diagnosed with OCD - reading about the experiences others have had with 'Pure O' has helped me to better understand these difficulties, but I've still got a way to go before I can tackle them.
I'm really sorry to hear you're experiencing this, as I know from experience how difficult it can be. I don't know if this is something you'd identify with personally, but I've found it's something I struggle to open up about to others, for fear of being taken as 'too intense' or 'crazy'.
What, if anything, have you found helpful in trying to deal with obsessive thoughts?