Just thought of something else about birth control pills in general. There are many different varieties of BC pills out there with all kinds of mixtures of estrogen and progestin. Different combinations provoke different reactions in different women. If you are worried about weight gain, then you should make sure your doctor knows, this will allow her to prescribe a pill with less estrogen or more progestin specifically to lessen that side effect. Same goes for decreased libido, water retention, spotting, etc. Some doctors may prescribe a pill for you, or give you a 3-month sample pack to see how it goes, and then expect you to report back with list of any side effects you have experienced. If you have any, then she should change your prescription. It is possible to take birth control pills with a minimum of side effects, finding the right pill is key. Don't just take the 777 scrip she gave you and figure you're stuck with it.
Hope that helps.