There are some key questions, your age, weight, metabolism, how effective exercise has been before, your general diet, have you always had a big bum or has it just crept up on you recently??
Sqad is right though, squats and lunges are a relatively high impact core exercise that you must be physically fit to undertake. Depending on your natural shape and metabolism some strict dieting combined with long walks, some cardio at the gym etc may work.
As another poster mentioned although women can have "problem areas" it is impossible to just lose weight in one area.
I would go with my first option and embrace it, providing it isnt getting you down too much!