When your child has a viral infection with fever it is normal to last around 5 days. Rushing to the doctor won't really help a virus go away. You should go to the doctor if your child has fever and is 3 months or younger, has a seizure, refuses to eat or drink, fever is lasting longer than five days, has trouble breathing, is not making eye contact, can't sleep and very fussy or other strange things.
Fever is the body's way of dealing with infections. The fever gets you to lie down and rest so your body can use its energy to combat the invader. Fever increases the bodies immune response. Reducing fever by taking medications such as tylenol or motrin can actually prolong the illness since the body can't fight it as well without the fever. There is nothing dangerous about fever, so generally there is no reason to take fever reducing medications. Don't worry about overheating your body regulates that it should not get too hot.
Fever is so beneficial for fighting infections that even artificially induced fever can help fight an infection. Many people head straight for the sauna when they feel like they are coming down with something and find that it helps.
It is also normal for kids to be cranky and not act themselves when they are sick. They will be tired and out of it because their body is mustering all its energy to fight the virus. Sleep is king when sick. This way the energy can be channeled towards fighting off the infection and not other things. This will speed up recovery time.
Another important thing to do if your child is sick-keep him/her hydrated. We lose water quicker when we have fever since we sweat more. So keep your child hydrated. Put a drop of lemon juice are similar in the water so they replenish electrolytes that they are losing. There are also mineral drops that you can drop in to their water to replace lost minerals. The main thing though is that they are drinking enough fluids. Coconut water is great. Chicken soup or bone broth is also a good fluid to take when sick.
You may also want to check out what homeopathic medicine has to offer. They can do wonders without any dangerous side effects.