5 and 3-year old vomiting every 3-5 days for 2 weeks

I have a 5 year old and 3 year that has been vomiting off and on for 2 weeks.  My daughter would vomit for a day, be fine for several days and then it would start again.  My 3 year old would vomit once, be fine the next morning and vomit 5 days later.  I don't know what to think.  The pediatrician said its viral when I took my daughter a week ago.  My 5 and 3-year old were even seperated for a week as one of them was spending time time at her grandmother's house and they both vomited this morning at seperate households.  They've never had any problems with certain foods or food allergies.  Has anyone ever experienced this? Any suggestions on where to go from here?

[Jennkcollins]

My 6 year is going through same thing. Ashe threw up Monday every hour from midnight till 8am today is Wesnesday, it's 11:30pm and she just came in my room throwing up again. I can hear her tummy growling but it's not from being hungry. I don't know why's going on, as she had this same thing 2 weeks ago, but that time she also had diarrhea.