Confused about dates, someone help lol


Okay bear with me.

From September 2nd to September 6th I had my period.

My periods are normally 34-35 days apart but for the last month they were 30 days apart.

Anyway, on September 18th and 20th I had unprotected sex.

I did not have sex any other time before that EXCEPT the day before my period.

I got multiple positive tests September 26th.

So when did I conceive? Is it even possible to get a positive test 6-8 days after unprotected sex?

If this is idiotic I apologize but when I do a conception calculator it says I would have conceived the how did I get a positive on the 26th? And not faint positives. Dark lines, positive digital etc.

Can someone explain this?

If I go by when I was ovulating it doesn't make sense because the egg would have barely implanted like a day again.

The only possible explanation was the sex I had before my period but online says that's impossible as my period would have just washed it all out.

Ugh I'm just trying to figure out my due date and when I can be seen which isn't till 8 weeks.