Too much sag in the back...
 

Since I got rid of my truck, my 98 4x4 4-door has been having to do everything. I bought a dirtbike hitch carrier for it, and it does get the bike around, but squats a lot in the back. Makes it handle a bit odd.

I really know very little about suspensions. I managed to change my shocks a month ago, and that was my first time doing anything related. I suppose I maybe should have bought some air adjustable ones at the time? Too late.

Is there a way to add another leaf, or helper spring?

I would like a small lift all around, so if that makes a difference in an answer...

yes you can add a leaf and its pretty easy to do. heres one place that sells them.
Rough Country Suspension ADD-A-LEAF KITS - JCWhitney

this will also start your small lift you are wanting, the leafs will add about 1.5-2 inches of lift in the back, then for the front you will either need to crank your torsion bars or get torsion keys. if you search this site for either of those two options you will find everything you need to know. but adding the leaf will for sure stiffen everything up