Could there still be a chance

Elizabeth • name is Elizabeth my husband and i have a boy and 2 girls with the hopes that we can get a boy as our last baby.
So my period it due today but nothing and no sign she is coming either. However I've taken 4 test all bfn I though I saw a vvvvvfl in one but maybe I was just seeing things the last test I took was Saturday. The only symptoms I have are nausea spells that come and go heartburn and headaches nothing else and I didn't have those symptoms when I was pregnant with my son. I took ovulation test and I got a positive on the night of the 10 and was still positive the 11th. Should I still have hope that i could possibly be pregnant and the test aren't picking it up or did I miss my window. Glow is pretty accruate about when my period starts off by maybe a day