Pregnancy weeks?

I don't understand this... I might be stupid or somthing lol but this is my first baby so it's confusing. I'm 29 weeks .. 29 weeks ago was my last period (oct21-25) so does that mean the baby is actually 29 weeks also? Or is she like 28 or somthing technically? I have a 35 day cycle roughly just trying to figure out if I conceived the week of my period or not..sorry if it's confusing lol