Kind of have some random questions about pregnancy in the first trimester

morganoo
So i just found out that im pregnant. It was about a week and a half ago on the expected day if my period. Its been confirmed by my doctor and the first day of my last period was march 11th. My doctor and the app is saying that im around 5 weeks but my mom told me that i would only be three weeks because i would have concieved around 1-2 weeks after my last period. So i was wondering what would be right? Also anyone else get cramping similar to menstural cramps the go away and i havent had spotting or anything else but im just kind of worried? Thanks for any answers you guys have :)