Please Please Please Help !!

Need your help friends. I'll give clear details first and then my concern.
I'm 27 yrs old; Married for two years now, TTC since Dec'2009 only. My cycle is 28-34 days.
My normal period started on 2 Jan' 2010,lasted 6 days.We have been sexually active post 10th Jan'2010.
Few symptoms that i noticed around end of Jan'10 were, lot of weeing/peeing, headache,heartburns at night(i never had them before in life) hungry and hogging all the time, burping a lot. Got a urine and blood(Beta HCG) test done on 6th Feb'10.Both negative.
I expected my period to start on 4th Feb'10. It started on 13th Feb'10 and lasted till 18th Feb'10.
But this was very very different frm my normal period.
During normal periods, i get slightly sore breasts (PMS) ,did not feel the same this time;
normally lil red in color, this time brown; normally blood, this time little blood with brown blood clots;
normally heavy first three days, this time light throughout;
normally get lower abdominal cramps, none this time.

Now my question:
Considering maybe i ovulated late in January'10, maybe around 25th Jan'10, and feritilation happend around 10th Feb'10; can this bleeding of Feb possibly be implantation bleeding?
If not, what possibly could be the reason for this kinda odd period, one that i have had ever before in my life?
Is it possible that fertilisation did not happen by 6th Feb'10, the date i got my Beta HCG test done?

I sincerely need help and your advices friends.. I am not sure if any faced a similar situation..Thnx in advance !!

[KeyD]

did you re test?