Question!!!???

Shayla • I am 26, hubby is 28 we are ttc our first child together! I have a 4 in a half year old from a previous relationship and she means everything to me. We just want to expand our little family !!!
Ok so I usually have a 21 day cycle yes its very short... anyways I am 4 days late but I am getting BFN with every test and I am not using the cheap ones! I am wondering if anyone knows of its possible I could be pregnant even though I am not getting a bfp since my cylcle is kind of short?