Yes I would see a doctor, it may just be implantation bleeding but you really should always be seen for bleeding. It could possibly be a miscarriage this early on. I did have the same thing ,it was almost like a normal period right when I found I was pregnant and I have had a healthy pregnancy. You need to get your hcg levels monitored by a doctor to make sure they are going up and that this isn't a miscarriage. Personally I would put myself on bed rest until you know whats going on.