My upper body is very thin,have tonned arms (I work as housekeeper),flat stomach, my problem is my butt?

I am 34, my butt is sagging, looks like pear with some cellulite on it and under my butt.Do I still need to do cardio since I do not want lose weight,since my upper body is so skinny. I workout 2-3 times a week only for lower body. I am not sure if I do it like I should!