How does it work?

Hannah • 16 years old, have been with my SO for 6 months now, he`s my life <3
I got told I could possibly pregnant and that I can get pregnant a week before my period. Does that mean this period that's coming up is it to soon to miss it only cause it was last week? I've had a lot of cramping and my nipples are a purplish brown it's not normally like this. Is it pregnancy ?