How do I separate three email threads that have intertwined?

I sent one email to two recipients. Then I sent a separate email to three different recipients. Then, much later, I sent a third email to several different recipients from the first two email. Some how the email strings, replies and re-replies, have all gotten together as though it is one string or thread. I'd like to know how to separate them back into three different emails with the right strings/threads attached.