How far along?

LMP was July 9th

After having this two days in a row, I called my doctors nurse line and was told to "tAkE tYlEnOl, AnD wEaR a PaD" because apparently this is very normal... however with my history of reproductive issues, I just couldn't settle for that answer.

Went to the doctor yesterday after having mild bleeding and clotting. Severe cramping... She checked my cervix and it was still closed and no noticeable damage. Also did a transvaginal and abdominal ultrasound, and found that there was in fact a intrauterine pregnancy. The sac in diameter of 0.9cm. Which is putting me less then 5 weeks gestation.

I do have a bicornuate uterus. Polycystic ovarian syndrome and endometriosis.

This is my first child, and honestly I have no idea about pregnancy and what to expect.

I know they add a week to how far along you are because it goes off the LMP, but is there a way that I am almost 5 weeks pregnant because she could find the actual sac on ultrasound? How does this work? How far am I really? It confuses me because before any of this, she said because I'm only about 5 1/2 weeks, it may be still to early to see anything... but they found something and it measured 0.9cm ....