Every time i bite down especially on something chewy i get a mild pain down the right side of my head. what may it be?

Strained muscle?: If the pain is running along the side of your head it is most likely a strained temporalis or masseter muscle. The temperomandibular joiint (TMJ) on that side may also have some internal derangement. Assuming all that stuff is fine then it could be a cracked molar. You may want to see your dentist for an evaluation. They should be able to determine the cause of the pain.