When will I get my bfp :(


My last period was aug 13-20 and I was suppose to ovulate on the 27th. We only bd the 23,25,26 and nothing since then. I’m now 18 dpo and 4 days late. And all BFNs on the expensive tests!! This is so frustrating. Let’s say I ovulated a few days late and it was aug 29 or 30. The sperm could have survived right? But if implantation takes 6-12 days.. then the latest I would have implanted would have been sept 8-11th so why haven’t I gotten a positive or even a faint line?