Within The Past Year, My Daughter Has Become Ill For

Within the past year, my daughter has become ill for a day or two about four times now, where it seems like a stomach flu, but the vomit has this same odd odor, very similar to yeast. She also has been chronically congested. Her O2 stats get pretty low at points throughout the night (as per recent sleep study results) and the mucous that comes from her nose is often green in colour. These could be two seperate issues or could perhaps be linked.