14 days late! Someone help please!

I have been with my boyfriend for over a year and back in April he asked if we could start to try for a baby and we have been having sex regular and been doing it on the ovulation days since then and my last period was 11th - 15th August and I'm now 14 days late for my period.

I took a pregnancy test on the 6th September and come back negative which was really disappointing and then I waited till 15th September and was negative again... I don't no what to do or what to think my period is always regular but I'm now 14 days late does anyone have any advice for me please