Loestrin 24 Fe and pregnancy prevention

I recently began taking Loestrin 24 Fe because I actually stopped having my period. I have lost 80 pounds over the last 2 1/2 years. The Doctor explained that the weight loss had affected my hormone levels and advised me to take this pill. However, she also assured me that I would not gain weight. I have been taking the pill for two weeks, and I have already gained 4 pounds. I am a faithful Weight Watcher member and looking back over what I ate the past 14 days and how much I worked out - the weight gain does not seem possible.

Doing some independent research, this pill has the lowest levels of estrogen, supposedly meaning that it shouldn't cause weight gain like other oral contraceptives with higher estrogen levels. However, the scale shows different results and I also feel like I am retaining water. I don't want to appear "vain," but I have worked very hard for a very long time to lose 80 pounds. I do not want to see it creep back on because of medication, especially when I am only using it for regulation, not pregnancy prevention.

From reading earlier postings, I know some other people have had similar experiences. Did your Doctor change the type of birth control? Did you simply stop taking the pill and lose the weight? Does anyone have any advice? I really appreciate the help!