Many possible. Multiple causes are possible. Most common would be sinus disease, migraine, or eyestrain from overuse of the eyes for prolonged reading or computer use. Thyroid disease, growths behind the eyes, are much less likely causes. If the pains persist, you should see an ophthalmologist, and if the eye exam is normal, your regular doctor may refer to ENT or neurology.
Mutilpe causes. Tension headaches, migraine headaches, increased intracranial pressure, grave's disease, glaucoma, viral syndromes are probably all on the differential list depending your your particular circumstances. Visit your doctor to get a better understanding of your personal cause.
Anything. Headaches can come from fatigue, sleeping too much or too little, eye strain, sleep apnea, snoring, being dehydrated, having chronic sinusitis or allergies, too much caffeine or over the counter headache medication, high blood pressure or something more serious like a tumor. See your doctor and get checked.
Headache. Headaches that include one eye and the nose can sometimes be caused by sinus infections. This could also be a migraine or a cluster headache. However, one-sided headaches can sometimes be signs of more ominous things and should always be checked out by your doctor.
Multiple things. Altgough that could easily be sinusitis it can also be a neurologic headache. Cluster headaches are often one sided, in the eye area, last 1-2 hours, are associated with one sided nasal cogestion and tearing (although it's a bit more common in men) an evaluation by ENT (including a ct scan to confirm) will usually get you on the right track.
Tension headache. Muscular tightness or tension can cause a tension headache which can cause pain around the eye.