Indentation lines?

I'm a week late for my period and I've taken 4 test, all end up negative but at first I swear it says positive and just fades away. I took one again yesterday morning and it said neg so I got ready to leave and when I came back later that night I looked and it had this indent where a positive would've been, but there's no color. I'm confused and not really having many symptoms except headaches and some foods make me wanna gag. I was supposed to start on the 10th.