i think a lot of the areas youre looking demand dedication.
you are, as you've noticed, not alone in your feelings of ineptitude. i think that people go through cycles of feeling as though they are really good at their hobbies/jobs...things that are artistic in any way tend to be rooted in success in such a fluid way that it is very hard for people in those fields to feel contstantly assured that they are "good."
the most important thing you can do, as mentioned by others, is to keep at it. i think it would help, too, to try and narrow things down, or at least get a schedule of practice in these areas so as not to spread yourself too thin.
each person has their own schedule that works for them. for example: i try to write for a few hours everyday. it helps and, of course, i cant come up with good stuff a lot of the time but it helps keep me "in shape" so to speak.
im also interested in music...but theory is less signifigant to me than playing, so...i spend only a little part of my week trying to learn some theory but a larger portion of it playing various instruments.
this makes me sound like a psychopath who has charted every hour of my day for months to come...
but, really, any kind of lax pattern can help build discipline.