A short story collection by Chisako. The first chapter (7 mini-chapters) is the titular "It's Painful That I Have No Idea What High School Girls Are Thinking of These Days", and then there are 6 other oneshot chapters.
It's Painful That I Have No Idea What High School Girls Are Thinking of These Days is a completed manga by Chisako, first published in 2018. It blends comedy and girls' love. You can read all 8 available chapters of It's Painful That I Have No Idea What High School Girls Are Thinking of These Days online for free on MangaPulse; the newest is Chapter 7.5, added 2020-11-06. The series is finished, so you can read it from start to end in one go.