Hi Dear thanks for your question ,your periods were delayed for 8 weeks and after 8 weeks you passed, dark colored blood,Dear one reason ,could be you period are delayed due to stress
and now your periods have started ,the anther reason is that you did pregnancy
test too early before it become positive ,and now the slight dark colored blood which you have passed is threatened abortion
.and the third reason could be ,you have now become pregnant and this small amount of blood is implantation
bleed ,which occur some time at he beginning of pregnancy.for all these thing go for your ultrasound
it will clinch the diagnosis.