Hello, new to psychforums

Hi I was diagnosed with GAD (as well as depression and personality disorder NOS). I decided to register for this site after coming across this thread http://www.psychforums.com/schizoid-personality/topic77688-40.html when I was searching for information about my constant fantasizing/looping thoughts. I'm not sure if this is really related to GAD or not, so sorry if this post is in the wrong place.
Anyway I'm constantly fantasizing about different situations, having/rehearsing conversations, looping social situations I've been in and modifying how I really acted. I know none of it is real, that's not the problem. The problem is I don't feel as though I have any control over this. I also have two or three layers of looping , incomplete thoughts, or pieces of a song, or even just a weird rhythm (the "weird rhythm" is almost impossible to describe; it's like counting without numbers or keeping a beat for just a second and repeating it over and over again) constantly playing in my head.
This makes it very difficult for me to concentrate and although I've discussed my difficulties concentrating with my psychiatrist, I never have enough time to really get into WHY I'm so distracted. After we talk about how anxious I am and how depressed I am I'm out of time. I don't know, this sucks. It's been particularly bad the last couple of days.