Thanks for your query.
Relax pyroric stenosis is not related with present illness.
Your baby is having diarrhea
which is mostly viral in nature and settles in few days.
Most important is to maintain hydration.
Give oral rehydration solution sip by sip after each loose stool
,give coconut water.lemonade,boiled potato,curd,buttermilk.
Give lactobaccilus for 2 to 3 days and zinc for 14 days .
In case symptoms persist get your child examined by pediatrician
as stool routine and culture is required.
Wishing your child good health.