What's wrong with me? Is it normal?

I usually feel very sad for no apparent reason. I'm a teenager, so I was wondering if it's normal for this age to start crying for no reason or from silly things. And yesterday, for example, I've gone through something that I felt was really embarrassing, although it wasn't, so I felt sad almost all day, and in the evening I started being so enthusiastic and happy, but when I woke up this morning I felt sad again. I never thought it's a big deal, but i started wondering if it's normal to feel like this. So is this just a faze teens go through and wait until it's gone or should I do something about it?