Brown spotting and 4 weeks pregnant with a hx of m/c?

sorry for the details, but i have a hx of m/c i have had 3 consecutive m/c. i just found out i am pregnant again, around 4 weeks, i ovulate late so there is no way to tell until you can see something on the u/s. i have been diagnosed with a factor 5 deficiancy (heterozygous) when i found out i was pregnant for the 5th time (i have had one successful pregnancy 8 years ago) i started spotting brown, very lightly. i went into my doctors office and she did an u/s, and did not see a sac which was expected. there was no blood in my uterus and the prego cyst was there. nothing was in my fallopian tube either. no red blood just a very dark brownish/reddish spotting with dark brown strings of tissue only when i wipe. no cramping and i still feel prego (tender breasts, nausia, fatigue) and she also put me on 40mg of lovonox daily. the spotting is heavier at night. with my other m/c i did not spot...it was bright red blood with pain all 3 times...this time it is very different...but my gut feeling is that it will not end well...please help!