Pregnancy tests and missed periods?

Devon

Hi y’all! I was wondering if you could inform me on something I don’t really don’t understand. First, why do pregnancy tests claim to test ‘3 days before your missed period’? Meaning, why is it your missed period that it uses as a time frame instead of time after the date of possible conception. Like if I have sex 2 days after my period, why do I have to wait to test til my next period that’s 4 weeks away, but if I were to have sex 2 weeks before my missed period, I could test at the same time even though the former was 2 weeks earlier. Does the question make sense? Another question, if you conceived let’s say 5 days before a period, will you miss that period or the next one? What about the day before a period (even though that is rare, just hypothetically speaking) would you still miss the period that’s due the next day even though it’s so soon? Please let me know!