12 days late

Period is 12 days late, I've taken 3 test and one at the docs and all came back negative. I have a regular 26 day cycle that is almost never late and when it is, it's only a day or two. I've been feeling nauseous, and sleepy and super bloated with a lil constipation. The other day I had cramps but no sign of af. Also no sore breast which I usually get right before a period. I also haven't had any implantation bleeding. Is it possible that my hgc levels are just too low? What do you guys think?