Change your birth control pill. Because there are so many kinds of the pill, you may find one that doesn't affect your weight.
Eat more calories each day. If you increase your calories by 500 per day, you will gain a pound a week. Choose healthy calories instead of empty calories, such as refined sugar. To boost your calories, add cheese, nuts or ground flaxseed to meals.
Snack on nuts, seeds, yogurt, hummus or avocado between meals. This will help you increase your overall caloric intake, which should help you gain weight. If you don't have much of an appetite, you may want to change your birth control pill to one that increases appetite.
Limit your cardiovascular exercise when trying to gain weight on the pill. Participate in aerobic exercise, such as walking, running or cycling, 2 to 3 days a week for 30 minutes at a time.
Add more strength training to your workout routine. This will help you add lean muscle mass while on birth control. Include exercises for all major muscles groups.