Three years since I became an office lady. I'm not unhappy with my current life, but...
Literal
OL became already 3-years. Current life [to-に] dissatisfaction [subject-が] exist [it's not that-訳じゃない][but-けど]...
ＯＬ 'office lady' — a common abbreviation for female office workers, though increasingly considered dated. もう３年 'already 3 years.' ~訳じゃないけど 'it's not that... but' hedges before an unspoken complaint or wish. The trailing dots suggest restless dissatisfaction beneath the surface.