Late ovulation?

So normally I ovulate around cd10.. I used opks from cd8-13 and only got close to a positive but the test line was never as dark as the control line like it was last month.. I assumed I had missed my surge or something, BDed anyway and now I'm thinking that I'm 6dpo.. Woke up to pee tonight and got the urge to use an opk for whatever reason. Now it's positive! I'm currently on cd17 and I guess starting the tww all over again? Anyone else have this happen? My cycles are usually super short (20 days) so this is really throwing me off..