Should I get a breast augmentation?

I am 19 and I have been a competitive runner since the age of 13. I am now quitting the sport as it has caused too much stress for me. From so much strenuous exercise, my breasts have lost, or have not developed much. I feel very 'uneven'. I'm 5'8" 35-27-38 and 145lbs. lower body is very muscular. my bra size is a very small 34b. I wasn't going to go huge, but I do have a larger frame. I am not wanting to do this to impress guys, at all. I want to feel good about myself. I don't want to feel like a little girl anymore, fill shirts out, and wear pretty strapless dresses that would otherwise fall off my top! :X so opinions?