Can I give a 4th dose of Advil in 24hrs if I really need it?

Hello! I came down with the flu last week and my 4 year old seems to be developing symptoms today. He has been running a fever all day, has a runny nose, coughs, loses his voice and is shivering. He is not eating much. I still have Advil at home, but the fever is rising very quickly. When I give him a dose of Advil, let's say at 2pm, the fever goes down around 3pm and goes up again around 5pm. Normally, I alternate between Advil and Tylenol until the fever goes down, but I don't have any more Tylenol and there is no more liquid in the pharmacy near my house. The pharmacy is closed at this hour, so I already gave the 3 doses of Advil for the day. I am afraid that tonight he will not be well. What can I do? Thank you for your help!