My 12 Year Old Daughter Has Been Sick Since July

My 12 year old daughter has been sick since July with vomiting, stomach cramping, fatigue, diarrhea - she has a slightly high white blood count in August, the pediatric gastro dr. Put her on flagyl 14 days ago for 10 days and a probiotic bc he thought she contracted giardiasis while we were on holiday along the Oregon coast in July - the flagyl made her more nauseated but we continued for 10 days, and her stool came back negative for internal damage, but she is still sick. He feels like she has post GI infectious dismobility and only suggested probiotics and relaxation/ hypnotherapy - where do we go from here, still has waves of nausea, extreme fatigue, headaches, dizziness, indigestion, diarrhea and some burning in her throat, please keep in mind that she tested neg for ulcer, and celiac