cd38 but no bfp?

Gen
Help, any experience? 
I'm 9 months postpartum, my periods have been back for 5 months and have been irregular, between 23-33 days. 
Today is cd38! Tests are bfn.
We only dtd twice this cycle (trying to refrain as close friends wedding in 9 months abroad!), once on cd 17 without 'completion', sorry tmi. Again on cd31 (the full sha-bang).
Could I be pregnant? 
Any ideas on this one?
Late ovulation cd31? One final thing, I did a random opk on cd31, it wasn't positive but it wasn't as pale as I'd expect it to be.....