What Causes Cyst In Lower Left Abdomen Of A Child?

My Daughter is 9, she suffers from milk allergy and has frequent diarehea and constipation. She ofen has bouts of severe nausia and vomiting. Had her in ER yesterday. They found a possible hernia or cist in abdomen lower left of belly button. They said not ot worry about it and sent her home. Last night vomiting, temp 100, and not wnating to eat or drink. No bowel movement since Monday. This a.m. nausia, temp 90