I have had a headache since having prep work done before a crown. yes i was injected in my gums. why the headache?

Inflammation: The prepping of the tooth may have inflamed the nerve of that tooth. Do anti-inflammatory OTC meds help? If so, take them to help alleviate your symptoms. If not, call your dentist. Either way advise your dentist at the next visit.

Headache: You didn't mention where you had the headache, but being open for an extended period of time can be tough on the jaw muscles. this can result in spasms of the muscles that attach to the sides of the head. Could also be muscles of the neck that were stabilizing the head during the treatment. little movement during treatment can cause a stiff neck and headaches