A chem pregnancy doesn't have to show up a + on a test. I had one and af was a couple of weeks late and very clotty when it did arrive, it was heavy and then stopped for a few days then started up again a bit lighter but still a bit clotty then stopped and then started up again a day or so later again with a little bit of clotting and was lighter. These are classic chemical pregnancy signs. In fact it was very similar to a miscarriage I had at 6 weeks except the 6 week clotting was a little bit larger.