BFN??

hello ladies I'm little bit confused Af is now 3 days late and I have felt a few symptoms of pregnanc so I went and bought 2 asda pregnancy tests. The first one came up with no reading!! - annoying. Then the second was a bfn. Can anyone help me understand why my period is late if it's a bfn or could that be wrong or should I test again? I dont want to get my hopes up!