I'm sure everyone has had that occasion where they are in a conversation, then later at night they think about all the things they should have said. That's literally me every conversation.
I think this is really really common. Every now and then I absolutely nail it in conversations and other times I will think of what I should have said later, in the shower, or while strugging once again to get to sleep. Often for me it is something charming I should or could have said to a girl I found attractive, but you don't have this issue because you are married. I am extremely confident and charismatic once I have had a few hours to think of something witty and creative to say to a beautiful woman