I'm 20 and been playing the piano for some 5 years and, according to my teacher, I am technically quite good (I disagree, maybe he means it on relative terms), but have almost no musicality (this I agree with).
I have a quite serious problem with keeping a steady beat; I always tend to accelerate (I myself do not realize I'm changing the pace, I know that only through my teacher's advice).
Curiously, sometimes I try tapping my left foot in the hope of helping my rhythm, but in the end my foot taps the beat correctly but my hands go completely out of sync with it, and I don't even notice that - in fact, I can't even reproduce it consciously.
I've started playing with a metronome and have been getting better at following its lead, but as soon as I turn it off my rhythm starts going astray.
Another issue my teacher recently detected is that my dynamics are just as irregular as my rhythm; my phrases do not follow a correct development of dynamics (instead of, for example, growing and fading, they remain at a given level and than suddenly go ff or pp). I partly ascribe that to technical issues with hitting the keys with the right pressure and partly to not knowing what sort of dynamic curve would sound better.
To sum it up: I can hit the right keys with not much effort, but not in the right time nor the right strength.
My problem, in my opinion, is a chronic lack of musicality; ever since I played the guitar when I was younger I wasn't able to learn a piece by ear, while my brother did it very effortlessly. I also can't improvise, never could, and only seldom, mostly before falling asleep, can I "compose" a song (only mentally though); most of the time I don't even have any song playing in my head.
I'm aware psychology plays a big role in causing this lack of musical expression, but aside from suggesting me to see a psychologist, what should I do to solve these issues?