What Causes Spotting And Gooey Period?

I had my period at the end of Feb and decided to take a pregnancy mid March because I was spotting. There was a faint line in the positive and decided to wait a couple days and take another test. I have taken a total of 5 and they were all negative and finally got my period which was all gooey in early May. I'm not on any birth control but have no idea what could be going on