How Does My Period Work If I Havent Had My Missed Period Yet Does The Pregnancy Tests From The Dollar Store Still Work?

If i havent had my missed period yet does the pregnancy tests from the dollar store still work? - how does my period work

If I had my period and do not miss the Dollar Store pregnancy tests anyway? Then I took one and they said negative, and I feel really pregnant. Abdominal pain, nausea, strong odors. But I still have about two weeks after my time of waiting and I lutera as birth control two weeks ago. Is this possible?