There are new tests out that test as early as two days before your period is due. The tests show positive at different levels of HCG, so you want to make sure you get one that is sensitive. Check pregnancy websites for lists of sensitivity by brand.
But don’t panic if you don’t get your period and you still get negative test results. Most of my pregnancies have not tested positive right away. The last time, it took a super-sensitive test to show positive, more than five days late.
And sometimes, women get loads of implantation bleeding, mistake that for their period, and are pregnant anyway. Totally messes with the estimated due date.
I agree that there’s little chance of getting pregnant if your period is actually due two days after sex. Unless your cycle is messed up this month, just for fun, and you actually ovulated around then (in which case, your period would be late this month on its own). Your period shows up relative to ovulation, not the other way around. It starts in response to the post-ovulatory processes if you aren’t pregnant. Usually about 14 days after ovulation, but 10-18 days isn’t all that unusual, either. 2 days is unlikely, though.
I also just knew, in different ways. With Gabe, I knew because I got implantation cramping. It was early for my period, and I had NO pms symptoms, just cramping. I felt GREAT otherwise. I didn’t get nausea until weeks later. But I knew as soon as I started cramping. My best friend (who didn’t know we were trying, and lives 2 hours away), had an intense dream that I was, and called me to tell me I was pregnant, the day I got my official results from the doctor.
Next pregnancy was an oops, and I knew that one because of freaky surreal spiritual events. I met the soul, basically. Totally overwhelming experience, majorly messed with my worldview. I was also ‘informed’ at that meeting that whatever happened was right, and I was not to worry. I miscarried that one. And remarkably, didn’t worry.
Next pregnancy, again, I knew from physical symptoms, before my period was due, right around implantation time. No spiritual stuff that time. Just symptoms. Miscarried again. That one sucked massively.
Next pregnancy was a probable implantation failure, slight symptoms, stronger symptoms, then fading symptoms, and then my period showed - can’t remember if it was early or late but not the usual time, and didn’t test.
Next pregnancy, funky symptoms all over the place, no clear ‘you are pregnant’ but had a ‘feeling’ that I was. Tested, negative. Tested again, negative. No period. Waited a few more days and tested again, negative. Then went out the same day and got one of the super-sensitive tests, and tested again, positive. That’s Brendan.
BTW, there are a few Dopers on the StorkNet pregnancy message boards. If you are looking for a ‘club’, there’s always that one. No pressure. 