I'm in a similar situation right now, and I don't really want to go into the nitty gritty because I'm sick of discussing it offline, never mind online, but eventually they will leave you alone. I've found it hard when the teachers have been on my back, one even ringing up my home to check I wasn't anorexic, just because I was quite down and because I'm naturally thin, so that must be the problem type-of-thing. Best thing to do I suppose is try to not let it show (I should take my own advice!) that you're upset, and try to work the grades back up again. I'm like you - I thrive on encouragement, and like to know when I'm doing well, because I'm critical enough of myself as it is, so when a teacher starts having a go as well it can be quite crushing.
We'll live, let's look forward to uni!