how do you find post that you put up here weeks or months ago?

Click on your screen name. Then click "Find all post by Chatham".

More specifically:

Click your screen name at the top right

Then click on Statistics

Then click on all Threads made by to see the threads you made or click all Posts to see the different posts you have made

Also, when viewing the forum pages, there are icons on the very left which show you when you have replied to a thread. You can hover over it and it will tell you how many posts you have in a thread and when your last one was.

If the post was WAY back, it's probably easier to do it the other way it has been described.