My 3.5 yr ild sin woke up this morning with diarrhea, and he has had it all day long since, we noticed the diarrhea has a really bad dead fish like smell to it, all he poops liquids and some mucus i ve found in his underwear as well, he is been on the toilet quite often, withing a period of every 20 minutes in the last hour. He threw up once as well and it was all water as well. any advise?