Dates confused

I'm confused about the dates. I started my last period July 9. Ended around the 13th. Had sex around July 24 to 27. Then went to camp. Came back on Aug 9th , had sex again and again. And 6 days later i was spotting. Took a pregnancy test on the 19th of Aug, cause my periods are so irregular. Found out I was pregnant. But I'm wondering. Did I get pregnant before camp or afterwards ? Big gap there. Am I 7 weeks or shy of 4 weeks ? Plus I've been experiencing already the last week and half of nausea. Any opinions ?

Sorry forgot to mention : my first ultrasound isn't for at least two weeks