Help?

I have a bad problem with overthinking. Whether it's the past, future, or present I can't stop myself from thinking what's going to happen, what already happened, or what couldve happened. There's a few things that I try not to think about because I start getting a little depressed but my mind always goes back to that. One minute I'm happy with myself or even where I am in life and then the next minute I'm disappointed with everything. It's like I can't stop the negative thoughts that are constantly running through my mind. There have been nights where I have just been up because I'm thinking about something that had happened that day or already happened or just thinking about life in general. Its crazy because this has been going on for as long as I can remember and its really tiring now because my mood is constantly changing. Even as a child, I would always think about life and start contemplating on whats going to happen or just start thinking about the bad first before the good. I worry about things that are both relevant and irrelevant and it gets annoying because that when I start doubting myself and thinking of the worst possible outcomes. I start getting depressed and I get stuck in this gloomy state until I get myself out or someone or something cheers me up. I know it might sound crazy but I just feel like sometimes Im going through a mid life crisis and the sad part is Im only 22. I just want to be happy and have that peace of mind.