No period last month no cramping but now bright red spotting with grey tissue lining and a positive and two negative pregnancy test. why ?

Unclear: It's possible that you had a miscarriage or possible that you still have a viable pregnancy. A blood test 48 hrs apart would help you determine if your pregnancy was viable or a miscarriage. Or you can wait and see if the bleeding continues and a full period comes. If you have pain then see a doctor as wouldn't want to miss an ectopic pregnancy.