When the third molar was erupting so why pain reached to the head?

Referred pain: Dental pain can be referred to other regions of the head and neck.

Referred pain: When third molars erupt, they can affect the bite causing headaches, and diffuse pain.

Referred/infection: Either referred pain or infection. See an oral surgeon for assessment/treatment.

Referred pain: Pain anywhere in your body can be referred anywhere along the supplying nerve trunk. If you are having pain as you are teething, it may indicate a problem. You should be examined by a specialist Oral Surgeon for best advice as to viability of wisdom teeth, health of surrounding teeth/gums/bone, and a discussion of appropriate measures.