Weird Period Behavior

Samantha
September 2014 I had a period. From then until early January 2015 I did not have one. In those several months I took multiple (at least 6)  hpt's and all said negative. When I did have my period I noticed at first it was very very dark red. Is this old blood? And why did my period go away for so long?
Btw, I do have an irregular period.