Difficult to say. It's 'normal' with depression to obsess over negative thoughts but that doesn't seem to be the case here. It could be that you have anxiety with the depression which happens a lot as depression and anxiety like to hold hands. The anxiety may make you obsess over things that may not seem relevant but can be an escape from dealing with issues. The fact that you've been diagnosed in the past with a possible obsessive disorder often means that it does come back from time to time especially in times of stress or distress.