Periods twice in a month

Paulina • 23. Los Angeles. Mommy of a beautiful 7 year old boy and a two month old baby boy!
Hey girls! Quick question, is it normal to have my period twice in a month? I'm very regular and my period comes every month at the exact date it's supposed to and last for about 6-7 days. I'm freaking out because I got my period two weeks after my first period.. is this normal? 
UPDATE: I started my period again but it's not like the normal red blood.. it's a very dark red almost black color, should I be worried? This has only happened when I'm on the last days of my period. I'm freaking out and have horrible cramps. Any help would be very appreciated.