What might be the cause of frequent headaches?

Many. Headaches could be coming from tension, eye strain, tooth grinding, dehydration, lack of sleep/poor sleep, skipping meals, stress, sleep apnea/snoring, or chronic sinus problems.
Detox. If u have fillings in your teeth this could be interference field - let me know if u have fillings then u need heavy metal cleanse if not take magnesium supplements daily at night will help this.