i hate my body

i’m fifteen and i weight about 147 and i used to play sports and i quit about a year and a half ago and i feel that i’ve gained a lot of weight and i have this birthmark that goes on my neck all the to my arm. i’ve gotten really insecure with myself so badly that i only go out in jeans and a hoodie because i don’t like my arm fat or my birthmark. i have stopped wearing tang tops and shorts because of my fatness and i really think that it’s affecting me badly and it’s unhealthy because i’m beginning to hate my body more and more everyday because of how i look😣