cd 18 still no peak on opk

Kay
Hi all. So I have been taking CB digital opk since cd 15. Started with a negative reading, the next day up to today (cd 18) I have been getting flashing smileys. I normally have 28-30 day cycles. Is it possible to ovulate this late?! I don't think it's possible I ovulated earlier than cd 15 as no EWCM
I know I should've started earlier than cd 15 but oops lol 
Anyone had any experience with ovulating late in cycle?!?