I have what feels like a large vain under the skin behind rectum

so a couple of weeks ago i had a case of internal hemorrhoids.  It hurt a lot so i used preperation H and within three days everything felt alot better.  last week after a bm i was wiping and discovered what feels like an enlarged vain under the skin right behind my rectum sore to the touch and seems to be lead into my anus.  lookin at it u can only see evidence of  a bump about the size of a pee.  Im a little worried  if anyone know what this might be any info would be greatly appreciated