Possible misscarriage or normal?

I am currently 4 weeks pregnant but for the first time, I've been bleeding. I have had severe stomach cramps all day. The bleeding started off VERY light.. But it has gradually gotten a little heavier, with a very small amount of tiny clots. I know some women actually get their periods while they are pregnant.. So is bleeding completely abnormal? I just dont want to believe miscarriage is the only explanation; this is my first child and it took a long time to.conceive..