Re: Lack of improvement?
There's no way to improve your listening but by doing it. A lot. I have fairly extensive musical background going to back to childhood and understand (in a "I can pass a written test" way) a good bit of music theory. But my ear is terrible. If you play a fiddle tune for me on mandolin and I try to duplicate it you'd better be ready to play it a good many times and slowly.
I'm no expert but based on my own experience I have a strong suspicion that you need to start with hearing chords and chord progressions. If you can't recognize simple "cadences" like V7-I (for instance a G7 chord then a C-major chord) for what they are, find ways to hear them in various contexts until you can. Then move on to I-IV-V7-I progressions and so forth. But that stuff's real hard to practice on your own, maybe you ought to get an ear-training (for Dummies) book and CD type of thing.
It's tricky. I can hear and identify the very simplest progressions like the I-IV-V7-I one that I mention and a couple others but that's about it. And I've put a fair bit of effort into it over the last few years.
The first man who whistled
thought he had a wren in his mouth.
He went around all day
with his lips puckered,
afraid to swallow.
--"The First" by Wendell Berry