I cannot control my emotions properly

I recently lost a friend group because of what I have said that I did not mean. This is not the first time this has happened I have lost another friend group before them. I say hurtful things that I don’t mean and realize it late. I feel sudden rush of any emotion but much more stronger. For example: a minor inconvenience and I am overly frustrated and upset. Or I randomly feel sad and remember everything bad that has happened in my life and think putting an end to all. But the next second I am fine. My friends have been dealing with it and they eventually got fed up and left me. I want to understand myself. I think I am at the lowest point of my life. I am frustrated because I am the way that I am. It’s hard to control my emotions and I feel unpredictable. It’s ruining my everyday life because even my parents admitted it that they feel hurt when I say things I don’t mean when I tend to get overwhelmed and feel strong emotions. I am still a teenager, still very young. But I think I need help. I have talked with my mother about scheduling an appointment but she says there is no one available. I regret cancelling the appointment we planned 2 years ago all because I thought everything was getting better. I am graduating 2 days from now and I am scared that my mind will get the best of me.