a23mckee, I was like that with my 3rd and fourth. I got symptoms almost immediatly with my 3rd, and just knew it happened with this one (my 4th) my hubby knew too though, with my 3rd he told me I was, but I was so sure I couldn't have symptoms that early that I told him he was crazy. With this one he came back from being at work for 2 weeks, and when I told him he laughed and said that the guys at work had just been asking him if he'd knocked me up again yet, and he told them he was pretty sure he had lol. Sometimes you just know. I actually never even took a pregnancy test with this one!
Trust your gut hubby and i were ttc after sex the next day i told him i know im pregnant. I just felt it. If you think you are you know your body you probably are. I felt swollen in my tummy the next day. It was try number 3 and he laughed at me when i told him i was right.
The same thing happened to me and i for sure thought it was implantation but it wasnt no way to tell until you have missed your period
If you have a regular 28 day period the 12th would have been part of your fertile window. And what you could be experiencing now is implantation bleeding which usually happens 7-12 days after sex some people earlier or later. Best thing todo is wait for your next period or 14 days after intercourse.
It could be any number of things. I would wait a little longer and see what happens.
I'm no expert because I'm a ftm, but I don't think you'd have symptoms that soon