3 kids throwing up for over 3 weeks with no answers.?

This is happening in all 3 kids over 3 weeks, but mainly Amelia & Isabel. They don't have reflux. Already tested negative for the intestinal bacterial infection. And the only food they are... eating is bread, crackers, broth, water, rice, no dairy...and they don't have Celiac disease. They currently don't take any medication... unless it is Dramamine to help with the nausea. They also don't have food poisoning. Blood tests appear viral, but duration and repetitive nature don't fit. Also, no fevers accompany this. They are well hydrated, but they have no color left in their face, occasional blue lips... but nothing in the air shows up on any environmental test. Yet, they seem to improve when we leave the house and worsen while home. Amelia has also complained of "cloudy" vision...can't tell if that is related or not. I do have all of this written down in a "diary" and am not seeing anything causal in the symptoms.