No one can diagnose you over the internet as being depressed or not. All I can tell you is if you don't feel yourself, then something is wrong. There are several 'self diagnosis, depression' quizes on the internet, but none make up for the care you can receive through a doc. They will all tell you to see your doc if you have more than X number of symptoms.
Eventhough these thoughts of suicide are not 'serious' they are of concern. Withdrawing from social activities, and feeling 'down' or not happy is of concern.
If you feel like you could hurt someone when you get mad, then you need to seek help now. Same thing goes for if you make a plan or seriously consider committing suicide.
What I suggest to you is to go see your family doc. They are much better at help you then anyone on the internet ever could (they have family history, you, ect...). You need to tell the doc everything you have said here, and anything else. They will be able to put you on the path towards 'feeling better'. You can also tell your parents what you are feeling, tell them that you think you need help, but you don't know what to do. I am sure they are more then willing to help you in your time of need. Either way you are gonna need to see your doc. It could be as simple as a mild chemical imbalance to something requiring more serious attention. In any case, your doc is gonna need to be seen.
Everyone feels 'blue' once and awhile, it's normal. When it lasts more than 2 weeks, or is accompanied by thoughts of hurting yourself or others then it is time to seek help.
If you find yourself in immediate need of help, call the police (or ambulance if you have hurt yourself), a suicide hotline in your area, a teen support hotline in your area, or present yourself to the nearest emergency department. There is no shame in seeking help. It shows you are brave, and realize you need help.
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