A hpt taken after your period was due is extremely accurate. It's doubtful that you're pg.
Breastfeeding can definitely play a role in having odd cycles. If I were you, I'd just wait another couple of weeks and see what happens. I bet your period will show up eventually.
However, you could call your doctor and see if they'll give you a blood test if you just can't stop thinking about it. My doc would make me wait until I was late for my second period before giving me a blood test, but some doctors don't have any time restrictions.
Good luck!
Do you know anything about the hcg count? I was reading about HPT and that most tests don't register below 50hcg/mL, but I also read that women could register anywhere between 17hcg/mL and 48hcg/mL 14days after the fertilized egg reaches the uterus. Does anyone know if this is true? I took 3 pregnancy tests at home with my first born before it came up positive. My hcg level was too low prior to the test, and honestly I probably would not consider the third to be positive if my husband wasn't shining a mag light on the thing saying, "there's a line, there's a line"! Also, I am very fertile, it seems like when my husband and I have sex on that magic fertility day, we make a baby.
-Lisa
http://www.babyhopes.com/pregnancy-test-sensitivity.html
That website lists several brands and their sensitivities. I used Answer Brand Early Result with a sensitivity of 25 miu's and got my positive the day after AF was due.
Any hpt taken the day AF is due, or after, is very very accurate but this is why they say to wait 2 or 3 days and test again, giving your hcg time to double. So if your hcg was something very odd, like only 10 miu's on the day AF was due, then you'd get a positive hpt within a couple days afterwards. The level increases by more than double every 48 hours (+/-) with a viable pg.
Hope this helps!
"research findings showed that first appearance of HCG (implantation) occurred 6-12 days... " (according to the previous website given". So, ovulation date is 6/11, that means that the fertilized egg could have not reached uterus until 6/23- five days ago. So, it is possible that I don't have enough hcg to be registering on an average hpt... just so I don't completely rule out pregnancy. I think it's always best to expect the unexpected. With my oldest, after the first two pregnancy tests that came out negative I had a late night of drinking way too much wine, just to find out the next day that I was in fact pregnant (or prego as my lovely husband calls it).