Got BFP, unsure how far along tho

I found out I’m pregnant this Sunday Sept. 3. I had tested the Saturday before, Aug. 26 in the evening because I felt weird and it was totally negative. According to my last period I am 7 weeks this week. My tests have all been super dark and I’m not testing with first morning urine. Wouldn’t it have shown positive last Saturday if I was this far along? Possible twins? I’m having cramps and lightning crotch already. This is my 3rd pregnancy. Any advice helps! Thanks!