What Could Be The Cause For My Breasts Having Not Developed Beyond Early Puberty?

Hi, please I am sad right now because my breasts are no longer growing again. After my first development of nipples and very small fats around it, my breasts remained like that and now I am 19 and I still look like a twelve year old. Honestly I m losing confidence and my self esteem is dropping. I just want to be able to feel normal. I am too embarrassed to live with anyone because I wear a padded sports bra which doesn t push anything anyway but it gives an appearance of small noticable breast. I am about to write my exams and I am coming from home. I am too embarrassed to live with anyone. I just want to be normal and wear comfortable breast wears other than sports bra. It s very sad and depressing at times. I need help