Hello. My 16 Year Old Son Has Had No Appetite

Hello. My 16 year old son has had no appetite for a week, which is very unusual. Yesterday he felt constipated, then threw up. Has nausea, headache, low body temperature (96.7 with oral thermometer) and has thrown up twice today. He's eating crackers and drinking ginger ale for the nausea, which he says helps some. Says water makes worse. Suggestions? Should he be seen by the doctor?