How can i stop repettitive thoughts/stress?

i have so much time here at work now since its so slow but i do realize i do not need to worry so much. i do know that worrying isnt going to make it better. i just always find something to compulsively think about. i wasnt always like this, started when it got very slow at work. when i get home, its not nearly as bad. do you know of a natural remedy or otc remedy for this? i just want to clear my mind.