Why am I having my period twice in a month

Last since my period on the 7/01/2013 had a period cramp just 3 weeks after my last period. now I have just started my period again on the 31/01/2013 I'm bleeding very heavily dark blood. I'm so confuse and worried. Last had an ectopic pregnancy on the 4/11/2012. I'm so worried. Questions in mind Could I be pregnant? Am I having a miscarriage? Why am I having my period twice in a month? Having my period twice in one month as never happen to me. I'm so worried plz help