Hi! Welcome here!
Sorry that you are going through this. Some of us differ in our results of going on drugs and coming off of them. The diseases themselves cause us more fatigue than usual since our bodies are being attacked. My Rheumy suggests a couple of naps a day for me, when needed.
I've been weaning off Pred. also for a few weeks from 7 mgs. I am not feeling any more tired(I'm almost always tired). When I hit 4.5mgs. the pain came back with force, so I went back up a bit and now back down at 5mgs. which seems okay for now. I've been on Pred. this last time for 6 years. More fatigue wasn't the issue but pain was.
I can't say for sure what is causing your new symptoms but by reading up on Cymbalta(I haven't been on it), I see that some of the common side effects are what you are experiencing.
dry mouth
drowsiness
tired feeling
mild nausea or loss of appetite
Other things can cause these also, of course. Perhaps others will have more info on this. I do hope that you feel better soon.