Highschools supposed to be the best years of your life? not for me?! i need help?

Well ever since high school started and i am still only a freshmen things have been hordenus. I had a few best friends in middle school last year in 8th grade. I originally wasnt supposed to go to the school that I am in now. Once this year started things were different. I guess i started to become lazy and the friends i was always with were not paying attenion to me and kind of like blowing me off. Like i was just "there" if you know what i mean. Then i got into a argument with this girl that i have known forever, and alll my friends took her side when actually she was the wrong one. I always ask my friends to do things and they dont anwser me, or they have other things to do with other friends. I get really upset because I am always left out. No one ever textes me anymore, no one tells me any new gossip, no one cares if i went to the homecoming game. I used to be considered pretty well known in my grade, and I dont know I am kind of fat, and maybe is this why people have been acting like that towards me because now that all my popular friends are in high school its like they are hyped off "pretty friends".I feel outof place and i want to switch schools, this has had a dramatic effect on my grades and I am a A student, i get so upset some days that i wont come to school. I also tried making new friends but they dont lke or want to do anything i like doing, like being school spirtied, going to the mall, etc. Then i see my friends away messages and they are all out, and i always ask them to do things i dont know im so upset. What should I do to help turn my grades around and have my friends, maybe it is about looks ?