Healthy diet for a fourteen year old female

Patient: Hi, I’m a 14 year old female who might be put on birth control because of iron deficiency and heavy menstruel cycles. I heard birth control can make you gain weight and I’m concerned. My BMI is 18.8 and I want to keep at a healthy BMI. I get plenty of excersise (I run cross country, I’m a competitive swimmer and basketball player) but I’m concerned about my diet. I have a sweet tooth that I need to get rid of if I’m on birth control. Can you please give me an eating plan of what to eat and not to eat to stay healthy. I’m 5’2 and 103lbs. I hope you can help me.