after period cramping and spotting

I finished my last period a week and a half ago. Everything was normal until exactly a week after my period had finished. I stated to get cramps  (they felt exactly like period cramps) 
And I noticed blood in my underwear. It wasn't a lot but enough to put a pad on. The next day the cramps had gone and the bleeding had slowed down and and gone a dark brown colour as apposed to red the day before. 
Has anyone experienced this before or know what might me going on?