TDL Always Negative?

I am trying to do more TDLs to get more practice recognizing my thoughts. I am bothered that my brain is focusing on negative thoughts more times than not when I do this. I am generally a positive person with a great outlook. I get done doing a TDL and I feel awful because it’s so much beating myself up. Does it have to be this way? Can I TDL my positive thoughts? Or, is this a sign I am suppressing all the negative thoughts? As I work on this will they eventually go more 50/50?