this might be abit late but just start writing.
seriously. every single week i see my ext 2 teachers i always whinge to them about how hard it is to start and stuff like that because it is. and they always give me this slightly pitying, slightly knowing and increasingly exasperated look and then say: "just write."
im doing a critical response (stuff on life writing and how there are issues with how ppl are represented in it) as well and it was really hard to get started. but i've just been writing down all the things ive been thinkng about as well as responses to the books ive been looking at. half of it, or maybe three quarters of it aint oging to end up in the finished essay (omg, i cant wait) but theres like a paragraph or two that will/ might work.
just start writing. even if you start by just writing down the definition of the beat generation. or what you really think of jack kerouac (is that a beat guy?) etc. etc. a paragraph a night and in a week youll have something to show the teacher...?
also teacher was like: just remeber, you're an hsc english student, not some phd academic in university. hmm... i dunno whether that was helpful but i hope the rest of the above was... g. luck with critical response!! ^^