NEEd BiggEr ?

ok ths is a random question but im 13 and i have small s a small b or large a. I have been exersing and lost pounds, i never really hade large then and now they seem smaller. My mom thinks that i am anerexic and was trying to feed me all of this junk food. I am happy to gain 5 pounds the healthy way. so can you help me, is their anyway to gain pounds but have a great body. I know about muslce but i dont know if it will enlarge my s . I love my lower body bellow the i look healthy with a little flab but above it looks like i was nichole richie. HELP!!!