Make time for yourself. If you need to study instead of going to get ice cream with everyone, then do that. If no one is going to the gym but you know you need to go, start going alone. Chances are people will see how happy it makes you and ask if they can go with you next time. If you just need alone time, don't be afraid to just go to your room and shut the door. Go AWOL for a weekend (well let people know you're alive), so you can refocus yourself. It is so easy at this point in the school year to get caught up in everyone else's drama that you forget that those things are very little problems in the big picture.
You need to put your happiness first. You are the most important person in your life. Think of what makes you happy and do it. Do what will make YOU successful. It might mean you have to say no to people and I know that can be hard but if you don't put yourself first, no one else will. The way other people view you starts with how you view yourself, and even if you don't have all your shit together (God knows I don't), if you start everyday and think "hell yeah I'm a badass motherf-er", chances are you'll have a better day.
And you know what? I hate when I have to be responsible for water bottles too, Mr. West.