Had root canal finished yesterday on #3 molar, have temporal headache since and pain when I accidentally bite down on or grind tooth?

Not Uncommon. If OTC pain meds do not help, give your treating dentist a call. Pain should diminish in a day or two.
Not uncommon. You just had microsurgery. It will take time to heal. Temporary restoration may be "high" and may require adjustment. Tooth will need a crown to help prevent fracture. Call your Dentist and report your symptoms.