18 male, in the same exact situation. I figured last night was just going to be another new years spent alone (I usually don't mind being alone) but then I found out through snapchat that every single one of my "friends", even one I considered to be a true friend, all hung out together without sending a single message to me. And then one of them sent me a direct snap of one of those shitty panoramic videos of everyone in the room... I felt absolutely betrayed and basically broke down. I was extremely pissed and had nothing to vent to, so I just blocked them all and uninstalled the app with no regrets. It actually felt kinda liberating. If they can do something like this so nonchalantly and then act all friendly to me at school then they're no friends of mine. Not sure what I'm going to say to them the next time I see them.
Anyways, sorry for the rant, but I know exactly how you feel. People suck.
As for your situation, I may have a few tips
Sleeping in is really, really unhealthy as far as depression goes. I find when I wake up early, get in the shower and sit in my pajamas blaring my music my day gets a whole lot better. Get 7-8 hours, go to bed early (8-11PM). You'll definitely feel the difference in the morning
You say there's no reason to get up, but then you say you wake up too late to go to the gym. Working out is a huge combatant of depression; even something as menial as taking a walk will help. It will really help with taking your mind off of everything, or when you need it, it gives you time to think things over. Also, exercise makes you really hungry.
As a foot note, high school isn't the be-all end-all as far as friendships go. I certainly found that out last night, and now I can't wait for college to start so I can blow them all off and start over. Making lifelong friends in high school is extremely rare. Most adult friendships come from college or your workplace, so don't be bummed if your "friends" ignore you
This was kinda long but I hope I might have helped a little, please reply/PM if you have questions or wanna talk. Our situations are really similar so maybe some discussion can be mutually benefitial