My Son Had His Wisdom Teeth Out A Week Ago,

My son had his wisdom teeth out a week ago, starting Sunday he developed lower back pain, vomiting and diarrhea. On Wednesday our doctor sent us to ER for dehydration. BUN and cantenine levels were high even after 3 bags of Iv fluids. We went home and he still couldn't keep anything down. He Had more blood work the following day levels proved but still high. Today he continues to have diarrhea. What can this be? Is the dehydration causing the kidney issue or can the vomiting a result of the kidneys?