But you are different; everyone is unique!
Your body is still developing, but if you finish up with small boobs it's not a health condition that needs checking out by a doctor, it's just the way you are. When you are older you can get bras to give you a bit more cleavage if you think you need it, but for now stop comparing yourself to other people.
If people are making fun of you, ignore them. Or try a retort of "my boobs may be smaller than yours, but at least I'm a nice person and don't bully others about their appearance."