Check your blood pressure! My doc said that side effect was definitely from the med and I didn't have it when I stopped. Be careful: these meds need to be tapered though.

You can check it yourself with a blood pressure cuff. Or ask a pharmacist. I don't think your doctor necessarily is the only one to ask. You might be able to take a calcium channel blocker instead btw.

Or look at the side effect list. Here is one on the list:
"dizziness, faintness, or lightheadedness when getting up suddenly from a lying or sitting position" as well as "hypotension."

Hypotension (low blood pressure) can also cause headaches because oxygen to the brain may be affected.