15dpo bfn temp still high

Hi all- I'm 34 and this is my second month ttc#1.  Ovulation on cd 11 was confirmed by opk and thermal shift.  Now I'm 15dpo, af was due yesterday, no bbt drop this morning and bfn with frer.  What's up???  Fwiw, we didn't bd after ovulation this cycle so if I o'ed late, unlikely to lead to a bfp.  Any ideas? Is it even possible to have a bfn 15dpo and be pregnant this cycle?  Appreciate any insight anyone can offer- thanks!