I don't know what's happening anymore

Im currently in 11th grade and I've been feeling different than my happy self since 4th grade. I've been struggling with feeling crappy, rarely happy especially with school. Just about everyday I wake up my stomach goes into agonizing pains which stays throughout the whole day and only stops when I give in to calling home or when I have no school on weekends. I usually find myself thinking I'm wearing poor clothing, I'm always wearing coats to cover my fat arms and everything I hate about myself because I think people are talking about me and laughing at me. This has caused me staying home for well over 2 months added up which lead me to recently failing 2 classes. I've been so unmotivated the past years that has caused me to lose all of my friends irl because I just cant commit to talking everyday or hanging out and have even lost interest in all of the activities I loved. I feel okay sometimes but thoughts of people looking at me as soon as I walk into school or go outside will be insane.