Positive test 19 days after missed period....

Hi, I just found out I was pregnant this past Sunday. I took a test 1 day before my missed period, 7 days after missed period, 12 days after missed period and they were all negative. Finally I took one 19 days after missed period and it's positive! Has anyone else experienced anything like this? This is my 4th pregnancy, my first one I gave birth to my now 6 year old daughter. A few years ago I was about a week late, took a test that came out positive but I was already spotting and had a miscarriage. I had another miscarriage in October at 8 weeks. I was 18 days late with that one when I found out I was pregnant. I'm worried but praying for the best!