So, does my approaching rut have to do with...?

Kang-woo went straight to the hospital to run tests. He had no reason to believe Ji-hoo's words but at the same time, he also had no reason 'not' to believe.

He ran the tests, hoping they would not end up with something he would have problems handling.

And then he waited till he was called by the doctor.

"Your rut is due in a month or so." The doctor said to Kang-woo's horror.

"It's due?" He asked. "Are you saying that I have no way to stop it or maybe push it back?"

"I'm afraid not, son." The doctor responded, handing him the text result. Kang-woo could understand next to nothing about it even though it was written in the same language they were both familiar with.

"And what does this say?" Kang-woo asked.

"It says your rut is due. And if you're lucky, it'll be a month and a half." He said and Kang-woo shut his eyes.

Why was this happening?