Over the last couple of days ds has been shaking his head (as we do when saying no) really fast. He is only 6 months and is not saying no. He does this when he is tired, about to fall asleep, or just any time. Why is he doing it? It is really freaking us out. Yesterday he developed a temp and I brought him to the drs today and she said his throat is red so maybe that's why he is doing it. Has anyone ever seen this?