Idea of why I could be bleeding?

I found out a little over two weeks ago that I am pregnant with my second child. I've been bleeding since the day I found out. I went to the hospital, they ran some test, and checked things out. They came back with three possibilities. One, I could be in the beginning stages of a miscarriage, but I don't have any pain or cramps. Two, it could be implantation bleeding. Or three, I could have a tubal pregnancy, but there is a sack in my uterus. A couple days later I made a follow up appointment with a OBGYN. They took some ultrasound pictures and checked me out. They said that my body is doing everything it should, my cervix is closed, and the baby looks fine (for what they can see with me only being roughly five weeks). So I still haven't gotten a straight answer. Just that everything is going ok. I go back in a couple weeks for my next appointment. I am still bleeding tho and it makes me nervous. I've heard that some people bleed their whole pregnancies, or have periods. I didn't bleed at all with my first child, so this makes me nervous. Just wondering if any of yall have any idea what it could be?