I used to get deep, dark depressions like you're describing, and they'd last for months.

I think my medication has caused me to cycle rapidly, though. I get an episode roughly every 6 weeks and they last 2-3 weeks at a time. My depression is much more intense during those 2-3 weeks than it was when it'd last a few months. I often come up with "plans" of how I want to kill myself, and I actually start researching where to buy my supplies. It's pretty severe.

I kind of wish my medication would take me out of depression instead of causing rapid cycling. So, I haven't found a solution either... but I can say that medication has made it worse!

But yeah, I was in the same situation as you. Hopefully you can find meds that work.