How can you tell whether you have depression or are just going through a phase?

It may very well just be a phase, but if you're worried you should get a professional opinion. Atleast do it if things get worse.

I think it's best to get a professional opinion if you can afford it, but generally if the symptoms last more than two weeks it is a legitimate problem and not just a phase.

You should never self diagnose. If you think that there is something, you should definitely go see a doctor. I am totally the same with the happy one minute, sad the next. Depression is about not having a reason to feel sad, but feeling it anyway. And it isn't always just being sad, it is a lack of emotion. Being depressed means loosing interest in everything and having no motivation to get out of bed. I dont know if you are depressed or not, but try carrying on for just a bit longer, if things are still the same you should ask for help, if things start to get better then it may just have been a dark spell. Hormones are all over the place with teenagers.

Doll it is a phase, a very long phase, we all have sadness in our life, I spent a year and a half but it's okay now I'm stronger & a better person now, PM me if you need to talk! Experienced gal here! - mads