I actually think implantation occurs between 3-12 days past ovulation with 6-10 being the average. However, it can take 1-4 days for implantation bleeding to show up after implantation.
In my case I believe I implanted 3 days past my 5 day transfer (due to a sudden sharp pain and cramp in my uterus that I also had with two other pregnancies) . I then had spotting on 7 & 8dp5dt along with a faint positive hpt. So…assuming I am accurate that would mean that I implanted at 8 days past ovulation/retrieval and had implantation bleeding at 12 & 13 days past ovulation/retrieval.
Also, it takes on average 2-4 days after implantation for HCG to show up in urine so in my case the implantation spotting happened to show up at the same time as my positive hpt since it was 4 days after implantation and it took 4 days in my case for the blood to show and also 4 days for the hcg to show up in my urine.
SO…I say all this to say that some get the implantation spotting earlier than 4 days and thus their hcg doesn’t show up in urine until 3 days after their bleeding does (assuming their bleeding shows up right at implantation). If this is the case then the HCG wouldn’t have been high enough at your beta because implantation wouldn’t have occured until that same day hence the spotting the day after and so…if AF doesn’t show up in the next couple of days I would retest with an hpt.
Having said all that though it may be still be signs of AF coming. Also, if you were on a progesterone supplement and you stopped taking the day before due to negative beta then it makes sense you would start spotting (even brown) and will eventually start AF.
If you haven’t stopped your progesterone then you could stay on it another 4 days and retest if AF hasn’t shown up just to be sure as delaying AF on a hope won’t hurt you (though it may be more difficult if it is still negative so…IDK).
Once you are 18 days past ovulation the odds of still being pregnant with a negative hpt are only 1% so not likely at that point.
Anyway, I hope all works out and if it isn’t this cycle 'ing hard with you it is the next! :grouphug: