How do you know if you have got depression?!?

i think i might have depression, i dont want to talk to a family member or doctor till i know for sure.

I feel constant tiredness, having to sleep all the time, blaming myself, always feeling guilty for something so little, stressing out easily, being very emotional (crying a lot and just emotional)

But when im happy I am fine and cheerful and happy and just a loving person and supportive person.

Is there anyone there that can tell me the signs or if i might have slight signs, because i hate feeling like this, and i just cant stop it no matter how hard i try to feel happy sometimes i cant, and i break down a lot.

It might be. Not everybody suffering from a major depression is constantly sad (you can google for "atypical depression"). And you can't know "for sure" if you don't get diagnosed.
If you need a justification to talk to a doc or a family member then yes, I think you should definitely do it.
Having said that, I believe a doc (even just a family practitioner) is better equipped to understand your problem than somebody in your family (unless he or she has some experience with depression) - they may simply try to cheer you up instead of getting some help.

I've had depression for about 5 years so I think I
know about this topic.

To me it sounds like you have most of the symptoms of it. Are
you like this every day? Because if so it definetely sounds like you have depression. Is your eating different? Are you uninterested in your usual activities?

I know how hard it can be but if you tell someone, things will most likely get better. If your not comfortable telling an adult, then at least tell a friend. I know it was really scary at first when my friends found out about my cutting and depression, but they've helped me.

Also sounds like a problem with your self-esteem
you need to talk to someone and get some type of support or help, a counselor can help you get more information

Do you have trouble eating-too much or too little?
You should consult a counselor if your life is unbearable...it doesn't hurt to ask!