Omg I'm 26 and just noticed I have cellulite it's really ugly help I'm only a size 5 and walk all day!?

I don't understand how and why I got cellulite on my lower and upper legs I don't go too the gym but I walk a lot at work and have always tried hard too watch my diet pls any quick fixes I just got cellulite I use too have beautiful muscular legs! Thanks!