Testing too early bfn.

How many of you ladies have tested to earlier got a bfn but tested a few days later with a bfp? I’m 8dpo on day 6&7 I had the worst back ache/cramping today I woke up no back ache but my boobs are somewhat sore. Which I don’t even get when af comes.. so my question is anybody get bfn on 8dpo and get a positive a few days later?