Do you think that there would ever be a chance to loose fat thighs and weight?

hey there well im almost 17 , im 5'9 and i weigh about 135 lbs , i do have a flat belly but it totally doesnt match with my legs ! i have fat legs and thighs , im just too embarrassed when i wear a bikini , anyway i have a gym membership and im that kinda person that admires eating vegetables , healthy things but at the same time i do eat 2 large Macdonald's meal , and i'm not gonna lie , sometimes i get obsessed and stop eating for 2 days , but usually i eat a lot like 3 meals a day and something between them . i'm thinking about joining a gym for about 2 months , what should i do there to loose weight and fat thighs and how much time do i need to notice a difference , oh knowing that in summer i do swim 3-4 hours a day .. thank you