I didn't see anything until 6 weeks even with the vaginal scan for this one. Also, I had ended up ovulating at the end of my cycle which is weird for me. So, I thought I was 8 weeks, not 6. Possible you ovulated or it implanted later than you think.
Also, I had an ectopic pregnancy prior to this one. I had no symptoms (besides a gut feeling). My doctor ignored my concerns and it ruptured at 9 weeks. I had to be rushed to another city for emergency surgery and I lost my left Fallopian tube. The ER was going to send me home for two days as they also ignored my concerns and if they had I wouldn't be here. So be sure to do all the follow up tests.
I had a scan done that early with my last baby an they weren't able to see anything I went back two weeks later an there the baby was my dr said I could have just implanted late but everything turned out fine