Hi! My Last Period Was February 13 And I Took

Hi! My last period was February 13 and I took a pregnancy test last April 13 and 14 and it's all positive. But last April 29, I was having a heavy bleeding with big clot. April 30, I went to my doctor and had a Transvaginal ultrasound but they didn't find any fetal, yolk sac and gestational sac. And also I've Anteverted uterus and thickened endomitrium. They told me that I'm not pregnant. My heavy bleeding lasted April 30 but May 1-7 it was on and off spotting. My normal period is regular and it lasted for 6 days only. So, it's my first time to delayed my period for 2 months. So,last May 7, 9 and 10 I was having a Faint positive line. What does it mean.