Firstly, thanks everyone!
There's some things I read which I didn't realize before, and do now, and will improve on :) And of course thank you for the comments too ;D
The reason the pulling in the head, is firstly he himself sometimes plays with the bit - and the reason for that, I know, is because I am also pulling on the reins. It's like I said, he's very stiff, so I have to bend him in, bend him outwards all the time, and sometimes he wont, and sometimes he does, but then his shoulders don't follow. Especially on the left side :/ I try using my legs and thighs, but no, my legs are not strong.. xD At least they are not strong enough for him - you really need legs to ride this guy! But yea, I try..
If I sit completely still with the reins and don't move my fingers, he will simply take
the left rein, and turn his head to the right! So when going around a corner to the left, he will push his left shoulder inwards and bend to the right..! Without me disturbing him in the mouth, and using my whole left leg to put that shoulder back in!
He's really hard to ride.. It looks easier than it is. But also, I had a new bit on him which is a little stronger, so I didn't dare make bigger movements with the reins, to bend him, as I would usually do instead of irritating small ones - I was a little scared to do too much since I'm not used to riding with a harder bit.
As to the choppy circles - yes, I know.. xD But we're working on it. It's because I'm supporting him on the outside rein, and then he starts leaning into it, thus pushing his outside shoulder out, instead of keeping it in. And the way I keep it in, is to support even more on the outside rein and turn him inwards using the outside rein and outside leg - But then the circles don't become smooth as he kind of "chops" inwards.. o.O
I've done a lot of work where I don't use the reins a lot, and have them loose, just to calm him down and make him relaxed - So he's not always too happy when I suddenly have shorter reins on him and where he has to actually work.
But currently, my biggest project with him is keeping him relaxed, having those shoulders where they should be, and having his head down - no matter if his neck/head are positioned right, I don't care, as long as he doesn't take it up. That will come later, with time. :)
Mollybolly: Yes I do have a trainer, and he's very good - my horse would not look like this if it wasn't for him, he'd be constantly stressed, running away from me, with his head up to the sky and mouth as hard as stone :/