Pregnant after an abortion?

Hello 4 weeks ago I had an abortion. This would of been my second child.i fell pregnant on the contraceptive pill.(Btw can't use comdoms) I got told by the nurse to go on the contraceptive pill while I wait for the marina coil. My hcg levels have taken a while tofo down since abortion.However last week I started to spot blood when I wipe. It was light pink and sometimes brown but wasn't much. That was on and off for few days. I have started to have symptoms again like I did before of pregnancy. I'd i am I won't get rid again. However how will i know if i am pregnant. I have all symptoms. But not sure how I would know.