Stool sample? 29 weeks pregnant help?

I went today to the clinic to get some papers. And I ended leaving with 3 tubes that I have to fill with my stool.

In my last appointment I told my dr I was having alot of braxton hicks, period like cramps and diarrhea. She didn't tell me nothing other than its normal. But today they told me dr. Wanted to do stool samples. But didn't tell me why. & i didnt get to see my dr today so I'm quite confused.

Anybody know what these test are for?