What Causes Diarrhoea Along With Nausea And Vomiting During Pregnancy?

I am on Zofran for pregnancy related nausea. I have had watery stool for much of my pregnancy. I am 23 weeks the past two weeks I have had terrible diarrhea and my nausea and vomiting is also on and off. I have been to the ER and to my OBGYN. All my tests and samples have come back negative. Could I be having this severe diarrhea from the Zofran?