At some point in your life, you are going to smile when you do not want to. You are going to pretend to be happy and put on a cheerful face for the people around you when on the inside you are screaming and crying and want to sleep.
I promise you are not alone and you do not have to pretend to be OK.
This is especially true if you are in high school, college or a young adult trying to get a job. I am very involved in at my university and the overwhelming sense of sadness that hits the students around me every year breaks my heart. As a generation of students, I see all of us trying to "fake it until you make it" like all those TedTalks tell us to, but at some point, you have to stop faking it.
I am here to tell you, it is OK to not be happy. It is OK not to smile. I am in the last week of classes about to start finals and I have resting sad face right now, and you know what? It's OK! I have given myself permission to not have a cheerful demeanor right now because I know my limits, I know that if I keep pretending to be OK when I am not, it is going to lead to a lot of mental health issues in the future.
Now, I am not saying it's OK to be mean to people just because you are having a bad day, but I am saying it's OK to not feel OK. Sometimes you wake up and simply feel off, let yourself feel off. If you have a terrible day, let yourself cry.
I guarantee giving yourself permission to have a bad day will make the good days even sweeter.
I can personally say I do not always take my own advice. I strive to be happy all the time, to help the people around me have the best day possible and to not let people know when I struggle. There are times when I do not allow myself to have a bad day because I do not want to seem weak or like I can't handle the burdens God has put on me. I can attest to the fact that those are the days I feel the worst. Those are the days I cry myself to sleep. Those are the days I pray selfishly instead of in a manner of serving.
Take my advice here and refocus yourself. Let yourself be sad for a day and then try to have a good day tomorrow. While you should pursue help with your mental health if you have lasting bouts of sadness or specific triggers, sometimes you just need to have a bad day so do not force yourself to smile and be happy. Having one bad day will lead to a lot more good days.
You will get through this, I promise.