Thanks @Silenus i like a challenge!! 
Well, I help people with resumes and sometimes professionals can get it wrong ... Mainly however I made that comment as you queried whether your CV might have been a problem in the past.
Discrimination towards consultants is not as common I would expect since consultants don't have to account for lost time, so maybe the issue relates moreso to your lack of desire to market yourself as you said in your first post.
And that's difficult, I was just chatting to @Former-Member about a coach ... have you considered a coach to help you with what appears to be not mental health issues but other barriers?
Just a thought.
Yes, you're right about companies not providing feedback (honest feedback anyway) but I do, so I know at least one person in this country who does 
...
When I completed my degree in counselling ... a friend also completed hers ... we both set out and I worked where I could. She began to get bitter about not being able to find suitable (read: interesting) work. Instead of griping about my first counselling job (which wasn't great) I looked around for how I could use what I had to create something ... I found it in a magazine article. From that article I formulated a program (very rudimentary) for women that I tried to sell, get funding for, give away to many people who did not want it. Then I stumbled across an organisation that did, they bought it and I never looked back. My friend is now unemployed and bitter about the degree we completed (both as mature age students) because it's not recognised by Medicare blah blah.
Why was I (and so many others) different ? We got creative.
You're a creative, technical writer @Silenus with passions and viewpoints unlike anyone else (you're unique) ... start a blog, start a forum, write for free for a NFP get creative about using your talents in ways that you've not tried before and see where that takes you.
It will at the very least give you some much needed exposure to potential clients or avenues which did not seem available or apparent before.
Selling may not be a strong point, but you have something to offer that others don't - find out what that is and just create the platform for it yourself.
Bipolar condition is manageable and I know clients who are able to work with the condition, successfully however I have noticed that they have had to reinvent themselves. I notice you were an engineer and now produce written work, maybe a new re-invention is in the wings ...
I also suggested working for companies that value 'lived experience'.. have you researched these orgs?
Challenges at work! Fun stuff!!
