I'm really sorry to hear that you are feeling down. You can always express yourself on here if you need to.
Can't you reduce the weight of your back-pack a bit. It shouldn't be making you ill!
As for your Mum, maybe she's going through a bad patch. Sometimes Mums say things, without realising the effects they might have on the kids. Try not to let it get you down. She probably doesn't mean any of it.
Remember, grown-ups are just kids who have got older. They make mistakes; they say silly things, etc. Of course, they have more experience, so I'm not saying that kids should ignore their parents, but simply that, if they say things that sound uncaring, it may just be thoughtlessness ~ in the same way that other kids can be thoughtless at times. There is no law that says adults must be perfect ~ and most aren't!
Yes, you are right that it certainly isn't healthy to think about killing yourself ~ but teenagers do get depressed because of their age ~ hormones etc ~ and this makes them very emotional & they become sensitive and respond to things differently from most children & adults. Things will get better ~ but if you seriously think of self-harming, do please tell your counsellor, or a trusted teacher or relative!! This is very, very important.
I promise you that many things that may seem really bad now, will not seem so bad when you look back later, so try to be positive. And please tell your counsellor about your worries, about any times when you have thought of hurting yourself, etc. He or she is there to support you. Don't you find him/her very helpful?
You sound like a nice, thoughtful & caring person, so think good thoughts and look forward to a good happy future.