Serum progesterone help

Belle

Hey guys. Bit confusing. Wondering if anybody would know what normal serum progesterone would be at 4dpo. I have irregular cycles and I misunderstood when my doctor wanted me to test it. My levels were 14 nmol (I think, I'm in Australia) at 4dpo. I ovulate on day 17 and I think Dr wanted me to test on day 24 but gave me a sheet that said day 21, so I tested on 21. (Which would be day 21 for a 28 day cycle). He said the results are low and negative for ovulation but I'm sure I ovulated, just wondering if anybody can clear this up, if it's due to having the blood drawn three days too early? Sorry if that's confusing.