If there's one positive step you haven't tried, try it.

If you haven't yet done what a few have suggested and see a good voice coach, DO IT!

What Robin said about not listening to doctors...
They know the mechanics, they know about the physical aspects. They are the luthiers of your voice.

A vocal coach or a speech therapist are the experts in how to play it. Your instrument is in about as good a shape as your luthiers can get it. Perhaps a teacher could show you how to get the most out of it.

Mary in Kentucky said talk to Alice. Alice seems to know a lot about voice and she seems to know a lot about specialists who deal with vocal problems. Alice is responsible for maintaining "Threads on the Singing Voice".

Please, try a specialist in operation of your voice before throwing in the towel. Over the past year, I've heard you sound just fine and I've heard you sound like you have a massive case of voice strain. It seems to me that a specialist might be able to help give you some contol over, and maximize, those 'just fine' periods.

At the end of the day, if you find singing's no longer something you want to do with the voice you have, remember that 'voice' is just how you express yourself. It's the 'yourself' bit that's important. Your singing voice is a tool and there are other types of tools, other types of voice. Guitar, books, stories for two. And you're a damned fine songwriter - write more of 'em!