What Causes Bleeding Twice In A Cycle?

20, 6'7, 125 lb. Hi, I had unprotected sex maybe a week or so before my period was due, I took the morning after pill straight away and got my period a few days later. It lasted a week and stopped for 2-3 days. But now I am bleeding again (bright red) of what seems like to be a period again even though I just had one last week. I was wondering what this means and if possible how long it could last?