My anus has been extremely itchy especially at night the last few days. every morning i wake up with a terrible headache and stiff neck. what could this mean? infection?

Pinworms?: One of the most common causes of nighttime anal itching is an intestinal parasite called pinworms but diagnosis requires evidence of their presence. The treatment is a prescription medication like albendazole. I can't think of any way this could be connected to your headache & stiff neck. So, in any case, you need to see a doctor.