!!!! HELP !!!! Cellulite at 17

I'm 17 years old, 5'6 137lb. I'm not overweight, I have a little bit of chub but I actually think it looks good on me. I haven't been getting much excercise for about a year and a half, home circumstances haven't allowed me out much and it seems like I've gained cellulite on my butt and thighs overnight pretty bad. I have smaller boobs and my butt was the thing that made me most confident but it's kind of flattened and now this. It makes me want to cry. How much can excercise get ride of it, or improve it? Especially because I'm only 17?