Period due but no period??

Amelia
My period was 1 day late! I took pregnancy tests and it was negative and this morning I thought my period came as I went to pee and wiped and there as blood and then later on when I needed to pee again there was nothing it was like old period blood trying to flush out 
I got my last period April 26th and I am taking birth control pills and my birth control pills in using is Trifeme and it says that if I'm taking them correctly which I am and I can sometimes miss a period whilst taking it should I just take another pregnancy test