Reading the answer to my nickname

My birth was probably related to water, so my gentle grandfather named me Miao 'er. I slowly grew up under the call of "Miao 'er, Miao' er." When I reached the age to go to school, my father felt that I should have a decent scientific name, so he gave me a popular name. However, my family still called me "Miao 'er, Miao' er." In particular, her mother called out especially loudly and frequently. I don't know why, but as I grew older, I felt uncomfortable hearing my family call me by my nickname again. It was as if I was being disrespected. Finally, one day, after hearing my mother call me Miao 'er again, I solemnly said to my mother,"Mom, I have a big name. Don't call me by my nickname, okay?" She walked into her room under her mother's shocked expression. However, her mother could not change her mind. It was my 16th birthday party that day. Many classmates and friends came, and the small living room at home was crowded. As I distributed candy to everyone, I thanked them profusely. Mom and Dad were busy cooking in the kitchen. When the fragrant dishes were served on the table, my classmate Ping brought me a big cake. I immediately thanked her and opened the cake box. I shouted,"Mom, bring me a knife!" "Miao 'er, be careful!" His mother handed him a melon knife and warned him. "Eh? So your name is Miao 'er. What a fun name!" Ping called out cheerfully, while making a unique gesture in the air. His friends also laughed in good faith. My face turned red all the way to my ears. At night, before I went to bed, I pushed open my mother's door. Leaning against the door frame, he said to her again,"Mom, didn't I tell you not to call me by my nickname?" There was a hint of impatience in his tone. Her mother had a complicated expression on her face. She looked at her father who walked in and sighed. Gao Xiang." However, I could hear that my name had become very stiff in her mouth, as if it was very difficult to pronounce. Soon, I will leave home and go to a city hundreds of miles away to study. Somehow, my mother learned to call me by my name in just a few days, and she was as fluent as when she used to call me by my nickname. Naturally, I am very happy. The day we parted, my parents sent me to the station together. My father kept nagging me, while my mother was silent and seemed a little sad. I smiled like an adult and comforted them."Don't worry. It's okay. I'm not a child anymore." The moment the train started moving, I stuck my head out of the window and waved goodbye to them. My mother, who had been silent all this while, suddenly raised her head, tears in her eyes. She ran quickly, waved her hands, and blurted out, "Write a letter back, Miao 'er! I was stunned for a moment, and my heart seemed to have been hit by something. Tears welled up in my eyes. I protested twice against my mother calling me by my nickname. What's the difference in the tone of these two protests? How was his mother's expression? How are you feeling?