My sister and i bumped heads and i got hit in the temple. now it kind of hurts to chew or open my mouth really wide. do i need to go and see a doctor?

Pain: likely just bruised that area and ice and time and anti inflammatories (if able to take) like Motrin should help. If you are nauseated/dizzy/ lost consciousness from the hit to the head... Go see a doctor. If not the first remedies should help but if persist then go see someone.

Depends on how long: This depends on how long ago- it happened. That muscle near your temple is connected to your chewing mechanism. If it is bruised, it may take a few weeks for it to go away