CD 41, Sparse Spotting, BFN?

Nicole • Twin boys conceived through IVF FET.
Hello. I'm CD 41, and 10 days late for AF. I've have some *super light* spotting off and on for the last three or four days. I've taken numerous HPTs and they have all been negative. I've never had a cycle this long. AF usually shows between CD 30-32. Any ideas? Could it be an EP? I'm under the impression EPs still give BFPs.