Self Confidence Issues, Maybe?

I may sound silly.. I have a bit of a belly on me but I don't think I'm obese? I'm roughly five foot five, and around 9 and a half stone. Over the past two days I have been called fat or tubby or a dumpling numerous times.. i am close friends with three girls, all of which are taller than me, better looking and skinnier, i am not jelous of them in the slightest i love them to peices, but often feel like i'm compaired too much to them? i have no idea what to do.. i am not putting my self on a stupid diet just trying to eat healthier, and i do a lot of exercise (a minimum of four mile walk with my dogs a day) ... what do i even do? :/ i can't just ignore them, but i don't want to feel bad about myself all the time. i've never ever been so 'insecure' :/