You should seek immediate medical care in an emergency room. The combination of focal neurological findings (such as drooping of the mouth) and severe headache is very, very concerning for a serious problem, such as a bleeding aneurysm or a tumor in the brain. In the emergency room, the doctors
will be able to perform a thorough neurological examination looking for any evidence of a residual nerve problem. They will also be able to go through your story with you in a bit more detail to see if it is an alarming in the details as it sounds here in brief over the internet. If they remain concerned, they will probably want to order some radiological studies of the brain to look for evidence of bleeding, inflammation, swelling, or tumor.
If all of those studies check out, then and only then will it be time to think about what (less serious) things might have caused your symptoms, such as bad migraine
or medication side effects. At that point your regular primary care doctor
will be able to help you, but you need to start with urgent medical evaluation to make sure there is not something really serious going on at this time.