Depends. A fever greater than 100.4f is the cut-off for qualifying fevers. If you have had one longer than 3 days and have symptoms such as pain, difficulty breathing, vomiting, diarrhea etc it is a good idea to see a doctor. You might consider going to an urgent care or your primary care doctor before heading to the emergency room.
Depends- call ur doc. Fever is due to multitude of reasons - viral/bacterial/fungal etc...Did you try tylenol/advil/ how old are you? How long has it been there? Have any trouble breathing? Stiff neck? Constipated? Muscle aching? Etc...If you still don't feel comfortable managing it, call your doc. Most have phone availability 24/7.