I've never been able to find the artwork tied to these descriptions
"One doujinshi manga (don't ask, NSFW—loli everywhere) features the loli girlfriend of some guy, who has her breasts surgically enlarged because she thinks it'll make her more appealing to him...but really, he only liked her because she looked flat-chested. So needless to say he's not impressed, yells at her, and throws her out. But she completely misreads this and assumed she's not big enough yet. At the end she's going back for more.
A similar doujinshin/hentai has a teenaged girl suffer a similar problem. Insecure about her size and wanting to impress some breast-obsessed boys who fawn over bakunyuu (read: big titty) manga, she gets an enormous boob job to meet their standards. But instead they get squicked by her huge chest and reject her advances. She assumes it was because her breasts are still too small, and tries going bigger, still longing for their approval. When they still reject her...she decides she needs to be even bigger.
Aaaand...different comic, similar plot: two sisters, the older one flat-chested and insecure the younger one comically oversized and boastful about it. After being humiliated by her "little" sister, who is still growing, the older girl decides to have her breasts enlarged...."
Would anyone have any leads?