Your symptoms suggest that you could be suffering from some hormonal
imbalance and this could be the cause for the delayed period. Yet, the risk of pregnancy
does exist as you had the intercourse during the fertile period if you have 30-day cycles. Since you had 4 negative pregnancy tests
this is almost ruled out. If you still doubt pregnancy, you can get a blood test
and a trans-vaginal sonogram and see your consultant for further evaluation. Take care.