What Causes Vaginal Bleeding After Getting A Positive Pregnancy Test?

Hi, I have a question about pregnancy. On Thursday afternoon around 3 pm I took a pregnancy test and it came out positive. Later on that night I went out and bought a different set of tests and around 10 pm I took another test and it came out positive. The next morning, Friday, around 6 in the morning I took another test and it came out positive. This morning, however, I went to use the bathroom and noticed bleeding or spotting. I didn t think too much and put on a panty liner. I went to work and the bleeding ended filling two panty liners from 4:30 am to 9:30 am. When I came home I took a pregnancy test and it came out negative. Am I not pregnant?