Maybe baby?

So my SO and I had sex a couple of weeks ago, and I want to say the day after there was a spot that looked like implantation bleeding. (Very light red dot and it only happened once and didn't look like my normal spotting)

Now I'm a week late and getting concerned not because there's a chance I'm pregnant but because I've probably gone overboard testing and I've taken a test every day of my missed period (minus like one or two) for a total of 6 tests, all done first thing in the morning, and one I did via a cup not just the stream. And every single one was a negitive.

I've had irregular periods in high school but they started evening out around when I turned 20 (I'm 22) I have been under some stress at work but not more than usual.

I'm calling my DR. tomorrow to make an appointment but I would like some ideas on what you think it could be.

I'm not taking BC and we aren't using protection. We weren't TRYING but we weren't really not at the same time.

Please be kind, and thank you in advance.