I’m pregnant and I’m assuming I’m 6 weeks 3 days going off my last period.

So the time we tried before this last time I was 4 days late for my period but then I started.. but I only bled for 2 days and then it was gone. My periods have ALWAYS lasted 5-6 days. Well I took a test anyway and it was negative, well this time I tried and took a test 4 days before missed period and got a pretty dark positive. Is there any way I could have gotten pregnant that first time? I see my doctor in 2 weeks so I’ll know for sure, just wanted to see what y’all think. ☺️