BAH REVISION!

So i've kind of slacked on the revision...maybe it's my lack of interest in psychology right now. To be honest i'm really not in to it as much as i used to be. I WANT to say that it's my teachers fault...and that probably is partly to blame. The week my first teacher left for maternity leave my grade in the class was an A. When the substitute arrived he immediately dropped me to a D and i feel like from then on in i haven't cared about the subject at all. At first i thought it might be a motivational thing, but now i'm not too sure...i mean, if the teacher wanted me to be motivated he would have given me a C, which is considered the average grade but most people want to be just above average. Having a D says 'you know less than average' and that doesn't motivate me at all...it just makes me feel below everyone else. A Failure, a mess, a wreck, a nobody. I feel like giving up on revision for the subject...i'm quite sure i'll fail.