My 7 yr old had a long period where she was in and out of the emergency room with vomitting.  It seemed to be a ritual.  We too noticed it was about once a month.  Its so long ago now but we remember that she'd end up with a hidden ear infection or a virus (probably from daycare or preschool). After a few days, sometimes after starting an antibiotic or after being admitted into the hospital she would be better.  She was on the liquid Cortef at the time and we were struggling to keep her levels on track.  We believe the frequency of emergencies have lessened simply because now she is old enough to tell us that she doesnt feel well and we can do something about it quicker.  Little tiny kids cant do that.  Good luck, I feel for you.  It seems like yesterday that we were in your shoes.  I dont know about the acidic smell.  Seems we recall the smell of "fishy crackers". Yuck!