Pregnancy

We are trying for a second child , i recently got a promotion 3 months ago & have been a little stressed out but according to this app I was supposed to start my period 7 days ago and I haven’t started yet . I know period symptoms and pregnancy symptoms can be similar , but I’ve been have mild cramping, back pains , Dizziness ( my head just feels weird ) but I have taken Two pregnancy test since my late period and Both say negative. Any advice on what could be going on and what I could try to possibly help us get pregnant faster ?