Not myself anymore

hello! i have no idea where to start. let's start with school. my grades, levels, marks, let's start with English it's the most important for me, lately my levels have been dropping, in English, science, RE, PE. English is the most important to me since i want to be an author  when i older.m I'm still in the top sets for most things. the problem with the whole top set thing is that my best friend (let's just say her names... Daisy) says that all the top sets are boring and lame. it may not seem like a threat or so bad, but if in my shoes you'll know how sensitive i am and how much that makes me feel, she's not the nice, funny, exciting friend she was when i met her. she's still exciting and fun but she cares way too much of what people think of her and she's always gossiping like and old woman. nest thing i just feel less, myself. like I'm not my "hello beautiful world! everybody's equal and everyone's special!" no not anymore. now it's just like "everyone's way way WAY better then me" i have no idea why. I'm just not feeling like I'm something. My favourite quote is "whoever mind don't matter and whoever matter don't mind" I love that quote because it's true, but that just doesn't seem to work for me anymore no matter how much i tell myself that i shouldn't think about what people think about me. I'm really confused and it's just not me anymore.