What could be wrong

Richaline
Hello everyone... I'm 23 yrs old.. I have a 4 yr old and me and my husband has been trying for over 3 yrs for another bundle of joy... I was supposed to start my period Monday, today is Thursday and still haven't started... and I've been feeling nauseated since monday.. I also took a test 2 days ago and it said negative. . anyone know what's could be going on