My understanding of ECT is that it kind of "rewires" your brain. I think if things get so bad you're getting no help, it may be worth a try.
I am personally on prozac and lamictal, which is an anti-epileptic used as a mood stabilizer. I'm bipolar, so that makes it a bit different than you, but depression is the worst for me- it's what makes me aim for whatever can get me back into the manic state. Drugs, sex, you name it. I wonder if lamictal would help you.
My psychiatrist and I had a conversation yesterday in which she asked me what would change if I could change anything since I'm almost but not quite satisfied with my meds. I told her I'd want my baseline mental state to rise a bit, have more energy. Ever taken prednisone? I've never felt better than I did when I was on that. She's added Abilify to my existing medications. Stay on an anti-depressant, and try adding that. You may need a higher dosage than average depression patients, like 10mg. This is your best bet, I think. I can let you know how I do with it too.

Good luck to you!