Need help with bruised tail bone?

ok so this may sound kind of stupid but one of my friends kneed me in the really hard and thats the hardest ive ever been kneed there and it really hurt and everytime i sat down it would hurt its been like three weeks now and it still hurts do i maybe have a bruised tail bone? or what should i see a doctor just to check it out or what? idk what i should do but please help thanks