Hey there
I'm sorry you feel this way, but you must remember that EVERYONE always feels down at least numerous times in their lives. You say your mates are there but they don't understand? Why don't you talk to them? Or at least talk to those you trust. I'm sure you're mates have problems of your own, please try and remember you aren't the only one feeling like you're 'sinking' others who you see and look perfectly happy could well have the same problems/feelings. Harsh problems? You're going to have to elaborate there im 'fraid.
Everything gets on top of you? Are you feeling particularly pressured right now? Look at what is causing that pressure? School? Family/friends? Or are you being too hard on yourself. Nobody's perfect
Glad to help,
Nat x