What Causes A Delayed Period And Stomach Cramps?

I have a fairly irregular period cycle from 30 days to 36. Only had intercourse once this month about day 14. I have done 3 preg tests as I am now about 4 days late (cd 40) and all neg. But all this month I have felt super tired and sick. My sense of smell has also increased. I had tummy cramps last week but no period yet.



I already have one child but got positive preg test result with him straight away. Could I be preg?. What should I do?.