Some birth control pills will cause more weight gain than others, depending on certain ingredients. If you look in the information on almost every birth control pill on the market, you will find weight gain as one of the possible side effects.
If you gain a substantial amount of weight or see your weight going up rapidly, talk to your doctor ASAP.
If you want to read to your heart's content on the subject, go to
www.google.com and enter "birth control and weight gain" in the search field. You'll be reading for months.
Have a great weekend!
P.S. I have not had any personal experiences with birth control. It's food that causes my weight to go up.