Please help me figure this out! 18.5 DPO no AF

[UrbanSimplicity]

link to chart below.

what i did not add to chart is that 13dpo i got a super light positive (not evap, it was pink but very light) and on 15dpo got a clear negative.  i did have a temp dip this morning.  now, on the evening of 18dpo i have one small quarter size stain on pad, only a stain, nothing else.  that was a few hours ago, still nothing more.  i never spot before i bleed.  i don't know how women do this every month - it is torture!!!  any thoughts would help.

<a href="http://www.fertilityfriend.com/home/2f03c8/">My Ovulation Chart</a>

[SilaMarila]

You could experiencing a Chemical Pregnancy. A Chemical pregnancy is when the egg gets fertilized but does not get a chance to implant into the uterine wall (endometrium). Since the egg didn't get a chance to implant, most women don't experience many symptoms other than a late period. With many sensitive hpts on the market today that can pick up very low levels of hcg a common symptom of a chemical pregnancy is a light positive hpt followed by negatives, followed by a late period.