When did you start cramping? Do you know when you ovulated? If you ovulated late, then your period be late. If you implanted late then you may not have enough hcg in your urine to test positive. It can take 3-4 days after implantation to test positive. When did you start cramping, today or a couple days ago? 3 days ago you can try to test with SMU or the next day test.

Mine hasn't showed up yet either and it was a big fat negative I'm going to retest in a few days if aunt Flo still hasn't showed up with a better brand test

I'm 10days late with bfn x