humm all of a sudden then bam it isnt the same..
well the best thing is to stop driving it so if theres more than just the clutch thats bad u dont mess it up also.
is it grinding and vibrating when u let it out or just vibrating. possible a broken spring on the clutch disk.
i assume ur car is a stock car what model. si hf dx
any history on the car before u got it.

any way u look at it probaly have to yard the trans out. what state u live in.