Strange thing happen could it be possible for me to be pregnant?

I have a very normal cycle which is 28 days my af always always since I HAVE HAD ONE was 7 days long and I'm not sure when i ov. but I think is usually 14dpo ok my last af was Nov5 and of course it was 7dys long and I had unprotected on the 15th that means I would've ovulated on the 18th i was my af came on time but it was light and then it was completely of by the 3rd morning. i took a test and it was negative right before af could i have had a late implantation? Is it possible that i could be pregnant? And will I get a neg right after af went off?