What Causes Headache After Titanium Plate Inserted In Skull?

I hope you can help. Im a 23 year old woman that was involved in a car accident 5 years ago, I had many injuries one of which was a brain hemorrhage resulting in me having a titanium plate inserted for 1/2 the left side of my skull. I suffer with severe headaches lasting for weeks at a times. What could be causing this? Please help!