The shapes are off. First, get your g/f, wife, that creepy yet willing girl next door, w/e to pose for you. Have them stand with their arms down at their sides, horizontal to the ground plane, straight up, and then in whatever they feel to be a comfortable resting position - get a full range and understanding of how a breast looks in the above poses. If the girl you get to pose isn't the same size/shape as the character you want, you'll have to improvise a little, but the same ideas apply.
If the girl happens to the be shape you want, get front, side, and top views of her - then use those three images as plates when you're modeling the character. If she's not (and really, even if she is), spend some time sketching and drawing out her form so that you're comfortable with the shapes and looks you want before sitting down in front of your screen. You can then use these sketches as your background plate for modeling.
Depending how detailed your models will be, or what your engine can handle, setup some proper lighting and take a picture of her back while you're at it to get a good base to start from for texturing later.