Failed as a mother

I’m going to be honest here. I don’t know much about autism. Where here I come from you keep them locked away until they are fixed because it’s not a real thing just bad parents. So I am trying really hard to learn what I can. I tried mumsnet but must have said something wrong because my whole account got removed. My son might be autistic. He is almost 15 so please understand that I’m extremely confused because I always thought it was something you get as an infant. He never showed any signs of being autistic. He is loving and speaks perfectly. He was always hitting his milestones and non of the schools ever mentioned anything was off with him. His primary school even had a whole other building for autistic children. He’s been having tantrums about silly things like not knowing what he wants to eat or the restaurant being too hot and noisy. Someone I know has an autistic child and she mentioned it too me. So I’m going to see the go in December with him to try get it treated, is it treatable? I know it can’t be cured but can they do things to help. My friends child won’t look at you, doesn’t speak and flaps his hands and screams when he needs something. I didn’t know you could get autistic teens. Everything is all written about babies and young children. So what did I do wrong? I believed that the MMR was safe and vaccinated all my children against my mothers orders, but I have obviously done something wrong. I have two other children and don’t want to make the same mistakes again. What did I do wrong? I followed everything my elders told me to do. We are supposed to go out with the whole family for Christmas but how can I take him if the doctors say he has autism? I know the minute my mother hears the doctor say he has autism that will be it. She will tell everyone I’m a useless mother and they will try take my others away so they don’t get it. I don’t want that for him. He’s a smart, lovely young man who just finds somethings difficult. Has anyone had to deal with this kind of thing. I just need help. I don’t even know how to tell my mother we have to take my son to the doctors and she is going to berate me for calling them without her permission. Am I doing the right thing? Is there anything I can use to show them that teens can get autism and that I am doing everything in my power to be a good mother to them all. Please I just need some help.