When I am in the 'mood' or feel inspired to write, it is only because, I realize that I have the entire concept down and really know it. Therefore, it comes more easily to express.
If you are trying to force yourself, then your level of concentration is getting in your way of being creative. Creativity is a guided action driven by ambition and talent.
You seem to have talent for writing.
You seem to have ambition for going places with your writing.
So, why do you limit your ability, by placing judgement on things you haven't yet done?
You say, "I don't think I can do that yet?". That's your problem- you are thinking that you can't do it, therefore you put your own blockade of your own ability.
Result, lack of self-confidence, lower amount of self-esteem to accomplish a task and an overall feeling of insecurity.
Learn to remove your own limitations by changing your view.
Positive attitude and faith in your own ability, is going to be the driving force of your life. Live it, Love and Enjoy!