Im 19 and havent had much calcium in my diet. im starting to take supplements to make up for the loss. are my bones still forming? im worried.

Hard to say: Calcium enters the diet in many forms. Milk, cheese of any sort and other dairy are the easy sources. Your bones are dynamic, building and remodeling constantly through life with length gains stopping in most females by 17+/-. I would be concerned if you broke bones easily, but not if you never have. Bone density studies could assess your bone quality.