How do you keep matters away from your mind?

I have this very bad habit of occupying my mind with unnesssary thinking usually due to problems I encountered in my daily life. I always feel guilty of my action and whenever i realise it, it is too late. I have a habit of rewinding almost every conversation i made to see how i reacted and most of the time i feel guilty of what i said and what i have done. It occured again a few minutes ago and I literally have something to say to this person whom I had coinversation with this afternoon but I will not be able to say it to him any sooner than next week. How can i remove this bit away from my mind, store it, and keep the information and my euthusiasm to speak to him until the time comes?