I SLIPPED ON THE ICE, LANDED ON MY LEFT BACK,

I SLIPPED ON THE ICE, LANDED ON MY LEFT BACK, HUGE KNOT ON MY HEAD, RIGHT RIBS HURT BADLY BUT AM MORE CONCERNED ABOUT MY BUTT. WENT TO ER SAID NO CRANIAL OR RIB FRACTURES SHOW. THEY DIDN'T LOOK AT MY BUTT. BY NEXT DAY WAS BRUISING AND SORE BUT SEEMS TO BE GETTING WORSE. PAIN IS WORSE, AND NOW HAVE BLACK BRUISES COVERING ABOUT A THIRD OF MY RIGHT CHEEK BELOW MY TAILBONE. SHOULD I BE WORRIED?