what does "I am not feeling up for it" mean? when can you use this?
I am not feeling up for it is not idiomatic to me. It appears to be a conflation of two different expressions.
I am not feeling up to it.
means "I am not well enough to do ...",
while
I am up for it
means "I am willing to take part in ...", with an implication that the activity is in some way challenging.