What Causes Vomiting In A 6 Year Old?

Hi. My son is almost 6 years old. Tuesday night he vomited his dinner. I suspected he had a 24 stomach bug that many people have been getting over the past month. His pediatrician always recommends a regiment of frequent sips of Gatorade until he can keep everything down for 6 hours. Twice after he vomited a small bit of mucus, then finally Wednesday afternoon he seemed well enough to eat - crackers, toast - small amounts. He vomited again late Wednesday afternoon & evening, so we repeated the process. Thursday morning he vomited a tiny bit of mucus, but by the evening he was able to tolerate foods. However, I noticed then that his temperature was extremely high - 104-105 F. I began giving him 10cc doeses of Children s Tylenol every 5-6 hours as needed. His pediatrician is out of town, and I spoke to a covering doctor. He said everything should be okay, as long as he doesn t have any severe abdominal pain, which he didn t. He is still going through a cycle in which he spikes a high fever, and Tylenol brings it down for about 4-5 hours. He also gets lethargic, sleepy and whinny when it spikes. He is about 90% of his normal self when the Tylenol is in effect. There are no other symptoms. I am concerned that this fever has gone on for this long. His ped returns tomorrow morning and his covering doctor is off today. At what point should I seek further medical attention? Should I take him to the ER, even though he feels okay when on Tylenol? (I m in NJ, where there is a deep freeze and would prefer to not take him out in the cold.) Thanks!