I am sorry you are going through this bad time. I have never been a JW or in a KH but I have worked with a youth group for many years. I agree with most of what is said above.
I would like to suggest a couple of things that might also help your switch to a more positive attitude. First please start a daily journal. Start by writing one or two things that you either noticed or experienced that made you smile. It could be your mom's dress or a flower. Maybe something one of your siblings did something that made you smile. As time goes by maybe instead of one or two things you might be filling that page with a lot of little things that have made you smile. Life is really about a whole lot of little pleasures not just one big thing.
Second thing I know you are being forced to attend all JW stuff by your parents. I read most of the programs or whatever it is called. I do not agree with any of it. Instead of being that flower on the wall. How about trying this out? Next meeting look around the room start with one of maybe the older sisters or another someone else who seems lonely. Walk up after the meeting with a smile on your face (even if you have to fake it) compliment her dress or her purse or shoes. Next meeting do 2 or 3. Adults just love it when youth give them compliments. Trust me it will make you feel better too. So spend the meeting time picking out your targets instead of listening to that boring crap then you won't have to stand there like a wall flower.