Did they check your progesterone level when they did your beta's?
I had brown spotting with my first baby for the first 3 months. It is scary, and with your previous eptopic I'm sure you are alarmed by the spotting. It's definately reassuring that you don't have any cramping or abdominal pain. Did your OB put you on pelvic rest? I avoided that completely during my entire pregnancy
My RE reassured me that the spotting was normal. I would ask for an U/S at the 6 week mark. As soon as I saw my daughters h/b at 6 weeks, I felt SO much better. Good luck, try not to worry girl!