Help please advice needed

[Alice535]

My question is can an ultrasound be off by a whole months cycle? Especially if done so early in the first trimester?

Blood test done 19th sept 2-3 weeks pregnant.

I had a ultrasound done 20th sept dating me at 4w 5d. There was basically an empty uterus but a cyst was in there. I didn't tell my doctor my last LMP I wanted yo be sure on the Us that it works. He said your LMP should be 18th august he was right I had a 5 day bleed then which I'm sure was just like my normal period.
I went back two weeks later and measured 6w5d saw a little jelly bean and a heart beat.
I had more US at 8-9 weeks 11 weeks 13 weeks 15 weeks 18 weeks. All measuring to the same due date given at the first US that matches to my LMP. May 25th.

So conception he said was 1st sept.

I'm not 31 weeks.

Is it possible that the bleeding could of been implation and they mistaked an 8-9w pregnancy for a 4-5 week one and that I was pregnant from my last cycle? And that all ultrasounds have been out by 4 weeks to a month?

Could this pregnant be from intercourse on august 2nd? I know sperm can live max 7 days so I took that into account for Aug 9 latest time of conception and still leaves a huge 3 week gap from the latest I cab conceive from that encounter and from the earliest I can conceive from my US and LMP 28 Aug.

surely if they are wrong I'll be due April 25th? Not may 25th ...
Could I really be 35-36 weeks pregnant and not 31 weeks.... I don't feel that far along.

If she comes close to her may due date can we rule it out? Thank you.

** before bashing me I used a,condom that night, it broke. I was separated from my current partner. And I couldn't get morning after pill because it was abroad. Got back with my current partner from the 12th august until present day.... Please help

** my period that came Aug 18 was actually due July 31st... But I'd had a cortisone shot for the first time and read it can throw off your cycles its a side effect.
I came off the pill in may and had two 28 day cycles