Late Period

I started spotting on December 18 and spotted VERY lightly off and on for about 6-7 days. By very lightly I mean only when I wipe, only enough for a panty liner. I was supposed to start AF on December 25 and didn't. I have taken about 7 pregnancy tests spacing them out by 2-3 days  and all have been negative. My stomach has felt a little uneasy and I have been slightly emotional. Those are the only symptoms. Has this ever happened to anyone else? Hormones unbalanced? Other problem? Could I be pregnant? Thanks!