Sick toddler, no answers

Ma

I’m desperate for answers 😞 about 3 weeks ago my 19-month-old began vomiting at night when in his crib. He also started having loose stools/diarrhea. We took him to the pediatrician who said it was a virus and told us to wait it out. After 3 weeks and not seeing much of a change, we took him to the ER where they said it shouldn’t last this long if it’s a virus but that it probably still is a virus and sent us home with zofran and a stool sample kit. With my poor boy loosing fluids and losing weight and is being unsatisfied with the ER visit, we took him to a children’s hospital the next day. They ran tests—white blood cells look good, blood tests are clean. They said the stool sample results will be most informative. They gave him IV fluids and he ate a bit of popcorn and drank a half bottle of milk while at the hospital. His poop the next morning (today) was not liquid but maybe like chunky mashed potato consistency? He drank more milk and ate a bite of a waffle and a couple blueberries. Since we’ve been told it’s probably viral/gastroenteritis I’m wondering if anyone’s kid has also experienced anything like this, how long it lasted, what you did, etc. I can’t stand to see my baby lose any more weight.

Thank you in advance ♥️