So the issue at the core, is your inability to fully access your inner world in a way?
It's not just you, I am similar... I firstly never really can access what's going on inside of my head.... and it's so very interesting that dominant Fi's can have a problem putting thoughts together in their head, along with verbal expression. I don't know about you, but now that I think about it... my stream of thought in it's natural form, is so abstract, and whimsical, to the degree that I very easily forget the world around me in away, and exist in a kind of dream land that I don't wake up from until I become conscious of myself.
Anyway, from Jung's psychological types;
The depth of this feeling can only be guessed–it can never be clearly grasped. It makes people silent and difficult of access; it shrinks back like a violet from the brute nature of the object in order to fill the depths of the subject. It comes out with negative judgments or assumes an air of profound indifference as a means of defence. The primordial images are, of course, just as much ideas as feelings. Fundamental ideas, ideas like God, freedom, and immortality, are just as much feeling values as they are significant ideas. Everything, therefore, that we have said about introverted thinking is equally true of introverted feeling, only here everything is felt while there it was thought. But the very fact that thoughts can generally be expressed more intelligibly than feelings demands a more than ordinary descriptive or artistic ability before the real wealth of this feeling can be even approximately presented or communicated to the world. If subjective thinking can be understood only with difficulty because of its unrelatedness, this is true in even higher degree of subjective feeling. In order to communicate with others, it has to find an external form not only acceptable to itself, but capable of arousing a parallel feeling in them.
Thanks to the relatively great inner (as well as outer) uniformity of human beings, it is actually possible to do this, though the form acceptable to feeling is extraordinarily difficult to find so long as it is still mainly oriented to the fathomless store of primordial images. If, however, feeling is falsified by an egocentric attitude, it at once becomes unsympathetic, because it is then concerned mainly with the ego. It inevitably creates the impression of sentimental self-love, of trying to make itself interesting, and even of morbid self-admiration.
Just as the subjectivized consciousness of the introverted thinker, striving after abstraction to the nth degree, only succeeds in intentisfying a thought process that is in itself empty, the intensification of egocentric feeling only leads to inane transports of feeling for their own sake. This is the mystical, ecstatic stage which opens the way for the extraverted functions that feeling has repressed. Just as introverted thinking is counterbalanced by a primitive feeling, to which objects attach themselves with magical force, introverted feeling is counterbalanced by a primitive thinking, whose concretism and slavery to facts surpass all bounds. Feeling progressively emancipates itself from the object and creates for itself a freedom of action and conscience that is purely subjective, and may even renounce all traditional values. But so much the more does unconscious thinking fall a victim to the power of objective reality.
I think infps' may be drawn to art and self expression for a very important reason. Not necessarily because infps' value art and creativity; but because it is the only means for us to express everything that goes on inside of us. There is essentially no other satisfying, and appropriate means. Some forms of communication might come close, but not as close as "artistic avenues". I'm not an artist, but my friend got me to do a writing project with him for a year, and I came out of that year, with much clearer thoughts, self confidence, internal clarity, and self knowledge. I did not know myself until I started writing. Free writing in particular. It forces you to think like you write, and write like you think.