Are you able to check your blood pressure at home?
How high was your blood pressure when your doctor added the amlodipine?
If you are able to check your blood pressure at home, is there much of a difference in the blood pressure when lying down, sitting , and then standing up?
There are several issues to consider. Certainly, any medicine that is designed to treat high blood pressure can cause excess lowering of the blood pressure. This can occur in two ways. The blood pressure can be low at all times, called hypotension. The blood pressure may also be significantly lower when moving to a sitting or a standing position, called orthostatic hypotension. You stated that your symptoms are worse when standing up, which may be due to orthostatic hypotension. Amlodipine works by dilating the blood vessels, and although it causes orthostatic hypotension less than other blood vessel dilators, any medicine in this class can do this. In cases of hypotension, the usual response is to use a lower dose of the drug. In cases of orthostatic hypotension, it may help to drink extra fluids. Since the medicine dilates the blood vessels, the blood vessels can hold a greater volume, and symptoms may improve with extra fluid (to "fill up your tank"). It is also true that any medicine that dilates blood vessels can cause headache as a side effect, and as your body becomes accustomed to the medicine, this side effect will usually ease off. If the side effect is intolerable, it would require using a lower dose of the drug or a different drug. In your case, it would be reasonable to first try to increase fluid intake to see if the symptoms improve.
If drinking extra fluids has not helped, then the only other options available to you would be to try a lower dose or stop the medicine until you can talk to your physician.