pregnancy symptoms?

Cycles the last 2 month's-

14th June-20th June

30th June-5th July

15th July-18th July

5th August - the lightest pink spotting which last a few hours.

Due on the 13th August. Very constipated, odd twinges in tummy. Taken a test the last few days but all negative.

Losing hope. Anyone else had an 'implantation bleed'?