Welcome to the forums. Thank you for such an honest post. You are obviously very self-aware noticing what is happening for you. That insight is great (even if it currently doesn't feel that way).
I know how hard a change from primary to high school can be. In primary school you have a single teacher to form a bond with for the year. In high school, it's harder when you are going from class to class, and never really having enough time or even 1:1 time to forge a deeper connection with your teachers. I found it quite difficult too. And it can be daunting with so many older kids, as you navigate your way from being a kid to a teenager to becoming an adult. Please know that a lot of people feel that way. You've lost the security of primary school, so it's completely understandable, as well as not having your mother around.
In regard to your anxiety, you are experiencing some really severe physical symptoms of anxiety. You're not going to like this - but the best way to combat anxiety is to talk about it. The more it stays in your head, the more the cycle of anxiety fuels itself. You get anxious about X, then you are so anxious about X that the physical symptoms occur, then the next time X occurs you are already worried before it even happens so when X does happen, your body and mind are already getting prepared for the anxiety.... and on and on it goes. And the more it stays in your own head, you start to believe it because nobody is challenging your anxious thoughts.
Do you have a counsellor at the school you could maybe talk to? Or could you speak to the Beyond Blue chat line (1300 22 4636) or web chat to get some assistance with how you could broach the subject with your mum? Then you could look at seeing a psychologist to help you through this period (if you felt comfortable).
In the meantime, here is a link to a handout of the Vicious Cycle of Anxiety: https://www.cci.health.wa.gov.au/~/media/CCI/Mental-Health-Professionals/Panic/Panic---Information-Sheets/Panic-Information-Sheet---03---The-Vicious-Cycle-of-Anxiety.pdf
I really rate the CCI resources, and they cover a lot of topics from anxiety, social anxiety, rumination (over thinking bad things). They might be able to help you understand your anxiety more, and give you the confidence to take the next steps of speaking with someone. You can find them here: https://www.cci.health.wa.gov.au/Resources/Looking-After-Yourself