Don't worry, I think every girl has a little bit of cellulite. I'm pretty thin and I still have it on my thighs. Here is my advice:
Don't really overwork yourself, but doing exercises that target the area can be really helpful. I have it on the backs of my thighs so I find even just running can help a little. Tightening up the area, even if you're really thin, can make it less noticeable. The thing I think that really helps is creating more circulation in the area. Try using a sponge in the shower in a circular motion on the area for a while. Cellulite is basically hardened fat, so anything you can do to try to break it up will help. Just massaging the area will help.
There are tons of creams and lotions out there for cellulite: I don't really think any of them get rid of it, but they have ingredients that tighten your skin ( like caffeine) so that it's less visible. That might be helpful when you want to wear shorts. Hope this helps!