The more I look into it I can't find a specific reason. My best guess is that it's just unfair luck, so I increased the chances to get pregnant within the house.
Seems to be working well on 0.1.8 for me.
I hope that other characters in the game world are planned to eventually notice and react to the MC being pregnant. MC's parents or siblings don't really seem to notice/care currently. Would be nice to see surprise, shock, anger, from the family depending on who the father is the first time they see her (or tells them prior to showing). Even perhaps continued support/doting from MC's mother if MC decides to keep it.
Other than identifying the father and telling them, the only other choice is whether to keep it or not. And then the restrictions on what you can't do as it progresses.
When pregnant, there seems to be one day in which you can still drink. It doesn't seem to count as a "day" in the 14-day term so maybe that's why? Not sure if that was planned or an oversight. Where it says in the quest log:
Pregnancy Quest
You found out who the father is! Should you tell them? Maybe you shouldn't, and rather end it before it's too late.
You can still drink at the bar. If the rest of the days are restricted, perhaps Day 0 should be as well.

I tested it but getting the pregnancy test done the morning it noted she was feeling off. The DNA test was done that afternoon. I didn't test if you don't notice if she's pregnant or not.