How many days have you been taking 300 mg of Wellbutrin? I suggest informing your psychiatrist about the symptoms you are experiencing. It is common to get jittery and anxious the first couple days after a dose increase of Wellbutrin. The fatigue and weakness sound different though, so definitely check in with him. If you've only been on the 300 mg for a few days and it isn't unbearable, perhaps give it a week. Side effects often subside within a week. Also, you are on a very high dose of Cymbalta. Does your psychiatrist intend that you stay on 120 mg Cymbalta and the 300 mg Wellbutrin, or is he thinking to stop the Cymbalta and just stay on Wellbutrin?

Stimulants are sometimes used for treatment resistant depression. I have taken stimulants for ADHD and they definitely lift mood.

Some other ideas for adding to the Cymbalta instead of the Wellbutrin: Mirtazapine or Modafinil.