Hello, Beverly II, and welcome to airforums.com
The rear sag issue is one that has come up many, many times on the forum, as a result there is an incredible anount of information here as to what to do, what not to do, and so on.
In order to unlock the information vault, all you have to do is look up to the top of most pages (like this one) and in the dark blue bar, over towards the right of center, you will see the Search button. Click once, and voila, the search menu is displayed. I personally like the Google version, it's faster and very complete.
Just now, I put "rear sag" into that box, and it came back with ten pages of threads.
Get a pot of coffee, and start reading through them. Enough patience, and you will "strike gold"!
If it's to be, it's up to me.