Going to school, being social and just doing life, in general, can be overwhelming and exhausting. A lot of times, we take it out on other things. We ignore the issues going on and instead of confronting them right away, we push them out and let things build in our mind and in our hearts. Sometimes when we hit the breaking point, it can truly feel like the worst day/week/year of our lives. I promise that if you confront whatever is going on, it's going to make a difference.
Start simple. If you get a midterm back and you didn't do as well as you thought you did, don't let it eat away at your happiness that day. Do something about it. Right then, right there. Whether it's emailing your professor to go over whatever your mistakes were or even just going through old material to help you prepare for the final, I guarantee you're going to feel better about it.
Maybe it's something bigger than that. Maybe it's your friend group and they don't really seem like your friends anymore. Please, please, please, do not ignore this feeling. Talk about it to someone. It doesn't necessarily have to be your friends, it could be your mom who might have more advice than you'd think. It could even be a counselor. Talking to someone who has no idea who you are or what your friends are like can be life changing.
Don't be discouraged, because you CAN and WILL overcome whatever you're going through. The first step is realizing you need something different, and addressing it as soon as possible is going to change your mindset on whatever the circumstance.