venlafaxine to sertraline to venlafaxine again or cymbalta?

Hi i'm trying to think through what to do next with my drug treatment.

I was on venlafaxine for well over 5 years and during that time I really began enjoying life. My energy levels, although hampered by the poor quality of sleep you get on venlafaxine, were good. I've since made the switch over to sertraline and feel like i am degenerating physically. Although I am beginning to feel less anxious, I have zero energy or drive to do anything. I just want to pull the curtains and hide away from the world. There's also been next to no improvement of my depression. I had a recent assessment by a psychiatrist who gave me 'recurrent depression (current episode moderate), GAD (this is a new one to me!) plus residual borderline traits'. Lovely.

I've certainly been a drain on the NHS in recent months, something I would never have dreamed of doing while on venlafaxine but for some reason my body began withdrawing from it (brain zaps, deepening depression etc), even when I was taking my 225mg every day without exception. Right now I'm considering going back onto it to give it another try now that my body has flushed it out of my system. Has anyone tried going back onto venlafaxine after it stopped working and found it beneficial? I'm tempted to push for cymbalta (also an snri) through my gp but he may be hesitant as I've heard its a lot more expensive than venlafaxine. Any ideas or success stories?