Reduce some of the things that stress you out.
Reduce some of your friends, find a hobby.
So you're stressed because of your marks and how your friends react to how you laugh? :/ Well then I suggest you tell your parents the truth. They might not exactly get what youre going through but I'm sure they'll have something to say about it. Btw, is the school NUS?
What about a new crowd? I did some volunteer stuff before and found awesome people through it. They make good friends really. Such a shame I can't be with them as much as I want to anymore.
Do it its bad to hold it in...shout let it all out...go to a quiet beach even if you need to take a train to get there and sream or scream into your pillow so not to disturb others ..cry your eyes out into that pillow cause it brings out toxins that build up in the body when you hold anger or saddness in. Once you let it out look into a mirror and you will be suprised at the state of yourself and probaly laugh and youll feel much better