Early spotting with twins?

Hi all! I'm 5w today and last week had my HCG levels monitored (following a mc in August). My levels quadrupled in 48 hours and when the nurse read the results she acted shocked and told me "there might be two in there!" I've been spotting brown, sometimes light pink, for about a week now. Just curious if anyone experienced continuous spotting early on in twin pregnancy? I'm not really cramping, just occasional "twinges" that alternate from the left to the right side.