I continue to get really bad headaches, what are some possible causes?

Probably migraines: The most common cause for frequent headache in an otherwise healthy individual is migraine. Oftentimes these can cause nausea, light sensitivity, and fatigue in addition to the pain. There are good treatments available--you might benefit from going on a preventative agent to reduce frequency/intensity of pain, and an acute agent to take when you get the headache (ie a triptan ie imitrex).