What Causes Vaginal Bleeding During Pregnancy?

I am confirmined pregnant,went to er because i was lightly bleeding but no pain.I was sent home and returned 48hrs later for a check in my levels they increased but so did the bleeding,no clots ,and no pain.My mind and emotions are set on overdrive right now from worry.I found out I was pregnant before my period so I'm confused as to why I had what appears to be a period.I am however slowing way down on the bleeding and still feel pregnant I have also taken another home test just to reassure myself.I know this is not normal but also not uncommon.How long is too long and how much is too much.