[Tiva]

Birth control can cause it and you may want to talk to your doctor, I know that some of my past birth controls have caused some lovely side effects including but not limited to weight gain, huge emotional mood swings, and severe cramps. They suggest trying it for 3 months and if it doesn't even out state it to your doctor, but some extreme things you need to tell then immediately.
Also if you are on a generic birth control you may have to switch pharmacies, as they typically carry only one brand of generic for each main birth control prescription Alesse = Lutera, Portia, Aviane, Amethyst