What Causes Vaginal Bleeding After Starting New Pack Of Birth Control Pills?

I had taken my pill late one day this month and since then i had my period one week early. Which i had it for about 5 days. So i started a new pack. Ive had slight cramping for the past few days...and now woke up this morning to find i was bleeding again. Im hoping im not pregnant, could this all be because of the pill i took late. Ive never had a problem with my cycle before. Thanks