My last period was Feb 26th and I'm having most of the pregnancy symptoms and urinating like ever 30 minutes but I took hpt @ 8 days late and it was negative. The day before yesterday I started spotting just a little and had lower back pain but then yesterday morning when I got up and went to urinate there was still just a very small amount of blood on my liner but when I wiped there was a long stringy type blood clot on the paper. What could that be ?