I've had a mild headache for the last couple of days that goes away with tylenol (acetaminophen) but comes back no other symptoms. what could it be from?

Many causes: There are many causes for mild headaches. Some causes include dehydration, smoking, alcohol, illegal drugs, too much caffeine and not enough exercise. Try increasing your water intake and getting rid of all caffeine and alcohol and getting more exercise such as walking. It is also possible that taking pain medications daily can cause the headaches.