how should I save my social life?

Currently I'm in high school and I have one friend that I have only hung out with a few times. Last year I had many more but this year I have no classes with them and I lost most of them due to false rumors spread about me. I really want to have friends but I feel like most people at my school are jerks. I also really want to get a girlfriend but I feel like nobody likes me. I'm decently attractive and people that actually know me say I'm extremely nice, however I am decently fat (actively losing weight.) People will say in front of me that they don't want to sit next to me. My friend is not at school every other day due to some stem program he's in so half the time I sit by myself at school. There's three things keeping me from switching schools: My friend, model UN, and fear of asking my mom. She's always known that I've had a rough time socially, so she's very patient with me and will gladly support things I do with friends any way she can. Am I the problem? Should I switch schools next year? What do I do? I really want a social life and a girlfriend.