Shin Tennen Kajuu Sayaka

From MangaHelpers:
Tsuzumi Sayaka wants to be a 'normal' high school girl, but she has a dirty mind that gets her constantly aroused. As a result, she feels like she lacks self-confidence, even though her butt and enormous breasts gain her a lot of attention. It seems she has to fight becoming aroused in any situation, even in teaching some supplemental lessons for her peers or trying out the judo club. Of course, not all of the situations she finds herself in are innocent--there are also men who snap photos of her butt and sketchy situations, such as the time that a shady man tried to recruit her as an 'idol'. Sayaka has a hard time navigating her high school life, but at least she has some good friends on her side to help!