You have social anxiety. You are fearful of interacting with people. This is not contestable. You need to ask yourself why you have social anxiety? If you already know why, and still haven't been able to help yourself, you need to confide in someone about the way you feel asap. To me it seem like you don't want to help yourself. You are making yourself a victim by not taking the steps that you know you need. It is obvious you feel bad about yourself, but in spite of that, it makes you even sicker to think about the things you will need to do to get out of the rut you are in. That
is the real problem, at least at this point in time.
You couldn't even tell your mom what you're going through. And btw, you should talk to her again. You didn't make a genuine attempt to reach out to her. You cannot expect her to feel the same way towards you as she would an arbitrary person you concocted. She does not care about that random child. She cares, I presume, about you. She does not want you to be weak. She does not want you to fail. Give her something to work with. You don't need to tell her you have social anxiety. Tell her you lack confidence because blah blah blah, or that you can't concentrate because blah blah blah, or that you hate that you are this, this, and this. You need to give her a chance before you convince yourself she can't help you.
Lastly, correct me if I'm wrong, but I think you suffer from social anxiety because you have self-esteem issues. And I know you won't take this to heart right now, but all the inadequacy you're feeling is made up. It's in your mind. You come to negative conclusions about yourself based on insignificant things like a person not sitting next to you on the bus.
I see people who say they have anxiety who seem totally fine even when they think you're not looking and it seems awful to say but I just feel like maybe I'm struggling internally more?
What does this mean? If someone knew you had anxiety and watched you when you weren't aware, do you think they'd think you're a shattered mess?
It doesn't matter if you're struggling more than other people. All that matters is you're struggling. Do not compare yourself to others. The constant comparing is a reason why you have social anxiety.
I found this website where you can anonymously chat with a psychologist about your mental health issues. I don't really know how great it is because I haven't used it, but it couldn't hurt. I saw some promising reviews online.
Before you can help yourself, you have to want to help yourself. I don't think you're there yet. So, for now, you need to think of how you can get there. I've listened to a lot of girls talk about their problems because I used to volunteer at a center dedicated to women's health. I just want you to know that what you're feeling is very common.