Two days positive then bleeding.....

I'm new to this group but I'm rather scared today and hoping I can find others with similar issues. When I was pregnant with my son, I was almost 3 weeks late before I has a positive test. I was "7 weeks" according to the Dr's based off my period. But when the checked the baby, he was only 4 wks in size and they told us he may be a miscarriage and after weeks of blood tests, ultrasounds and crying we found out he was fine and he was born perfect and on time.

This time I was 8 days late before I could get a positive test (I'm inpatient and took one every day) and then two days later, I woke up to a bleed. Red blood and egg white mucus. No pain or cramping and it has stopped since but I made a Dr's appointment but I'm so scared to hear the same thing over again--we don't know and we'll have to wait and see if it'll survive. Why does my body show positive so late and how do I know if I'm miscarrying??