Journaling is one of the best cures for overthinking - laying out your thoughts on paper not only clears your mind from repeating thoughts, it also allows you to notice your patterns of thinking, enabling you to act on them.

The easiest way to start is to write a single sentence of how you are feeling today. Ideally, in the morning.

For example - "I am feeling anxious today, because I had trouble falling to sleep as I was thinking about how to solve the issue that I was stuck on for a week"

This way you not only put your feelings into words, but also reveal the pain points that you have been dealing with - lack of sleep, thinking about work after work.