I'm sorry to hear about your struggles. I had really bad writers block a few years ago, and I didn't really remember until I read your post, but it coincided with terrible insomnia for me, too. I'm not sure how or why they'd go hand in hand. Maybe it's the exhaustion? In any case, I just wanted to say that it got better by itself for me, though it was very frustrating whilst it lasted.

The only thing that helped me (that wasn't something generic that helped the insomnia too) was to plan a story. It wasn't easy often and it didn't always work but it got my brain into a writing mode, and made it just that little bit more paint-by-numbers, which really helped when I was struggling. (And, of course things are difficult on three hours sleep, you know?)

On the one hand I really hate to say that maybe the years you've given it to resolve by itself isn't enough, but on the other I just wanted to reassure you that it can and will come back even after a terrible block like this. I hope your insomnia keeps getting better, too, and soon!