Weight gain after quitting birth control pil

I stopped taking the birth control pill about 6 months ago and ever since I have been gaining weight (and I have been losing my hair, but that's a different story). My diet has not changed, but I have gained 20 pounds. What are your experiences with this? When will the weight gain stop? I have always been insecure about my body and the way it looks now just makes me want to cry. What can I do? I have been trying to lose weight but it just won't come off.