Why so much Sadness?

In doing the very intense work on emotions this month I have realized that I am often feeling a deep sadness, that I have felt this way for years, and that I spend much of the day holding back tears. Sometimes I do cry, thinking that will lead me to relief, but then the painful sadness comes back again. The problem is that I can’t discern the thoughts related to this feeling. I try to paying attention to what’s going on when I am sad but I just cannot seem to discern any thoughts. Would love some suggestion on how to get to that step so I can start doing thought work.