Confused Guy Needs Help

I have recently found out I am going to be a father. On dec.9 and
dec.10 my fiance took 3 different pregnancy tests and they all came up
positive. On dec.14 she went to the doctor and they confirmed she was
pregnant. As we were talking about it she said the doctor asked her
when her last normal period was. Her last period was nov.10 but I dont
think it was a normal one. She said she had at least 3 abnormal periods
from sept.12 to nov.19 each 2 weeks apart.

I remember on nov.6 she took a pregnancy test and she said it was not pregnant. On nov. 22-23 she took an ovulation test and told me it was positive. We had sex the first time on oct.17 and didnt start trying to have a baby intentenally until oct.29.

We have recently had an argument and she left me saying we werent going to be together. I am going crazy now. She has also recently said she measured her stomach from the bottom of her belly button to her pubic bone and it is 14 inches, which would put how many weeks the baby is before we were together.

Someone please help me understand all of this. In a nutshell these where the events.

Sept.12 and after, she said she hasnt been with anyone but me.
Sept.12 - nov.19 at least 3 periods somewhere around 2 weeks apart.
Oct. 17 first time we had sex.
Oct. 29 started trying to have a baby.
Nov. 6 took pregnancy test said it was not pregnant.
Nov. 10 period started, stopped on the 14th.
Nov. 22-23 took ovulation test and she said she was ovulating.
Dec. 9-10 took home pregnancy test 3 came up pregnant.
Dec. 14 went to doctor verified she was pregnant.
Dec. 16 argued and she left me.
Dec. 21 she said she measured from the bottom of her belly button to
her pubic bone and it was 14 inches making her 14 weeks.
Putting the conception day back to:
sept. 14

she has not been on the pill at any time, and we havent used any protection.

Ok now, as long as she is telling me the truth about everything, which I wasn't standing over top of her when she did these tests because I trust her. There some issues that need to be addressed here.

I have read that you can have periods in your first trimester of being pregnant.
But we did a pregnancy test on nov.6 that was negative and she started her period on nov.10.
Would an ovualation test show positive for ovulating if you were pregnant?
Can you really go by measuring your belly like that and if so how accurate is doing that?

She is a petite girl. But this will be her second baby she already has an 8 year old.

As for symtoms:

late october she said she had started eating more, and would feel sick sometimes. But the sickness wasnt in the morning.

Around the first week of december she started saying that her breasts were hurting and aching.

Somewhere around dec.12 she started getting short tempered. But that could be due to a lot of things if it isnt moodiness.

She said she also had low blood pressure on dec.14 when she went to the doctor.

I hope someone can help me out with this and let me know what to expect.

Thanks,