Help with weight/ look flabby though im not fat?

i know that im a healthy size/ weight for my age and height (9 stone, 5'4) but my whole body just looks so untoned. im only 17 but i have cellulite on the back of my thighs and my ***, my stomach looks like a middle aged moms stomach to me. everything just looks so untoned even though ive never been larger than this, so there shouldnt really be excess skin.... what are some good toning up exercises? this just seems so unfair