Why do I get so angry and upset nowadays?

Hormones baby. But its good that you notice it so you can try to control it. Most people dont even realize it when theyre growing up. I didnt until i got older an looked back at myself. Its just your hormones. Youre at the age where you have, what my family calls, the "teenage funks" lol. So ur attitude will be a lil "funky" for a while but youll grow out of it. Mine was about 12-15. Puberty ages. When your hormones balance out youll start to feel normal again.

Thirteen, what a great age. This is when you start to realize that you have an opinion of what is good and what is bad. Your opinion matters, but you can't change everything or everyone, people do stupid things and though you feel passionate about the world around you, you must learn to except that instead of becoming frustrated. Just be a good person and lead by example, because things will get much more complicated in the years ahead, so try not to take the weight of the world on your shoulders and just be the best person you can be.

There's nothing wrong with you. I'm glad you have the good sense not to imagine you need therapy or any of that rubbish, that's a big point in your favour.

How about taking up a sport or regular excercise? You'll find you're much less aggressive after you've been cycling for thirty miles or done two hours of Krav Maga training.

I'm also 13 and this has happened to me before but for you it's most likely just mood swings from puberty

It's probably just hormones from puberty, relax, from the ages thirteen to fourteen it can get pretty bad, but you'll be alright.