Girls, Why have I lost so much weight?

I started birth control my freshman year of high school at about 120 pounds. I started it for acne. Almost a year ago (at 18) I decided to stop it finally because I was 150 pounds with acne still. Since then I have slowed dropped weight. Almost 20 pounds. Do you think it is from stopping my birth control? I also take Paxil but I vary my dose so much I'm not sure what it actually does to my weight. The only reason why I want to know is because I want to prevent it from coming back.
Girls, Why have I lost so much weight?
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