Weight Gain

Looking for opinions. My daughter was born March 8th and weighed 8 lbs at birth. She’s exclusively breast fed and has gained weight good until 3 months. At the end of May she weighed 15 lbs and now, the end of June, she still weighs 15 lbs. She seems very healthy and is hitting milestones but I’m just wondering if this is normal or I should be concerned before I call the doctors. She has plenty of wet diapers but usually goes a day or two without pooping. Thanks!