When the body temperature fluctuates up and down with a headache, it usually means that you have an infection.
You do not say what your gender is or how old you are, so I presume that you are not on the change of life.
Make an appointment to see your doctor. Take a mid stream morning urine sample too so that the doctor can examine that and check your ears, throat and lungs.
If the doctor finds that you have an infection that may be caused by bacteria, he will prescribe an antibiotic. Viral infections do not respond to antibiotics.
seek a doctor. Your having problems regulating your temperature. A flu should be making you have a high temperature(to burn the virus out) check your thermometer 91 is quite low for a core temp