Emotional breakdowns

Hey, lately I've been struggling with something. Anytime something really unimportant, something that doesn't matter at all happens, like my teacher talks to me in the 'wrong way' I end up thinking I'm freaking useless, dumb and will get kicked out of school- which results in me self harming. Or my mum came late from work and my boyfriend didn't answer my text and I ended up feeling like everyone around me is abandoning me and again- I self harmed. Does anyone else struggle with the same? Can you give me some tips on how to calm myself down when a situation like this comes?