Have you DTD recently? I always seem to spot brown after sex. Try not to worry, i'm sure everything is ok, although i know that's easier said than done
I personally hate Emergency rooms for pregnancy related problems. With my DS i went there because i had a gush of bright red blood (like 1c worth!). I went in, they checked my cervix and that was it. They said they wouldn't do anything else because i was only 19 weeks and there is nothing they could do anyway. The didn't listen for the HB, do an u/s or anything! I called my OB as soon as i left and they had me come in for an u/s. Moral of the story is, they can't do anything at the ER anyway, so i would wait until monday and call your Doctor unless you start bleeding bright red.
GL and KUP!