Positive test 1 week after sex

Long story short I had been spotting for the past 3 months (Irregular cycle) and then I stopped on May 5th. So of course 3 months of no sex WE HAD SEX all night. Exactly 1 week later May 12th I was nauseous all day so I took a test and it’s positive. How is this possible ? Im so grateful & Cant wait to meet my January 2022 baby. But has this happened to anyone else before? I dont want to get too excited.