How can I gain weight in your opinion?

I am 16 and I weigh 110 to 105 .. it varies uhm I feel I am skinnier than most everyone at my school! I am a sopomore and I still am an A32 .. my boyfriend doen’t care which rocks! but I still do. My sister is and 8TH GRADE! and she is almost a B! well.. she is my half sister, same mom and my mom has really small ones and I petite like me, no curves or anything :( I have improved a little in the weight thing but no boobs. I still feel really really self conscience all the time and sometimes people make fun of me but over the years that has died down a little. I just really want my legs and arms to fill out a little and want boobs but something easy. Is there anything like simple or even something I can try without going to the doctors that will actually work?