What causes a constant occurring throbbing reoccurring headache?

Many. Migraine is the most common, other like cluster headache, problem with sinuses, intracranial pathology may be considered. A neurologist will need lot more info to narrow down.
Many things. 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.