Very worried

Hi everyone! I need some help.

So, my last period started approx. 2/17/2021. I noticed I was late and took a few tests all negative, so I waited and by my 9th day of my missed period I got a very faint positive, then the 10th day I got another very faint positive, and now it says 13 days late. Yesterday I got a yes+ on a digital.... WELL, I went to get confirmation of my pregnancy because my app says I’d be 6 weeks today. Well the doctor decided to do a transvaginal ultrasound because she did a urine test and it was a faint positive.

Well she does the ultrasound and can’t find a single thing. No sac, nothing. Is this normal? At this point she said she couldn’t rule out ectopic because it was a bedside ultrasound.

She said it’s very rare so she believes I’m just way too early, but I was trying to calculate when I had sex last and I’d be 4 weeks 4 days. Is that too early or should I just expect an ectopic or miscarriage? 😪 she took my blood and said she’d call me tomorrow with my hcg number but I’m just so concerned. Why would I get a positive so late?:( would I have ovulated late or...? Please send some help or ideas? Happy thoughts!

Also, I had pulled a muscle in my back I think last week so i had severe lower back pain for 3 days. I have headache, mood swings and some nausea yesterday morning.