Have migraines but head is starting to really hurt for no reason now and one eye is dilated while other is fine. why would that happen to my eye?

Cyclical Migraine?: Partial or total ophthalmoplegia of the third cranial nerve, the oculomotor nerve, can occur during cyclic migraine. This may include pupillary dilation. See http://www.Headaches.Org/content/childrens-headache-disorders for a review. Nevertheless, if experiencing progressive neurological loss, you should present to an emergency room immediately. Otherwise, visit a neuro-ophthalmologist.