I understand how you feel, I have had a m/c at 13.5 weeks, this bleeding started out like spotting and I had lower ab. pain which felt like a heaviness pushing on my cervix. Over a couple of days this increased into heavier bleeding like a period, with more lower back pain and heaviness in cervix area.
With my two following pregnancies I had spotting-light bleeding for around 1.5 weeks at the 12-13 week period but without the heavy feeling, they were tense times.
hope all goes well for you