It is very difficult to build big muscles, both for women and men. Women don't have enough testosterone to build huge muscles. If you tend to 'bulk up' when you lift heavy weights, it's possible that you're simply gaining muscle faster than you're losing body fat. This is a common occurrence and you don't want to stop lifting! That added muscle will end up helping you lose more body fat so be patient, make sure you're doing enough cardio (3-5 days a week) for weight loss and your body will start changing.