I fear you're going to be out of luck. The workflow you describe shows that you're doing permanent destructive effects in Edit (Waveform) View rather than non destructive real time ones. You can only undo as long as you have them in History.
Audition provides for two ways to do effects. One is the destructive effects that you've used; the other is doing them in real time in multitrack view by creating an effects rack. Working this way in multitrack, the original tracks aren't changed at all and the effects are done real time each time you play the session. The only downside of this is that working this way is processor intensive and your computer will eventually run out of resources. However, if you get to this stage there are ways around it by "locking" the effects and so on.
If you DO use destructive editing, (and some effects are just to processor intensive to run live) it's a good idea to preserve the original. You can do this either by creating a copy of the original before you start work or by using the "Save As" command after each effect to change the name. I tend to give a descriptive name of what I've done...for example, Vocal 1 becomes "Vocal 1 proc EQ" then "Vocal 1 proc EQ Comp" and so on--but that's just my habit. However you do it, the goal is to keep your originals pristine.
....but working in realtime in MT view is your best bet.
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