Confused by LH surge

I've never posted before but have been reading the posts of others and have found them helpful as I am ttc. I'm wondering if anyone has experienced two LH surges within one cycle? I had a surge on cycle day 15. I was due for AF yesterday (day 28). I'm usually pretty regular so was surprised not to get it yesterday. I took an hpt that was negative. For some reason I also decided to do an opk and it was positive last night and this morning. Is it weird to have a surge on the day you miss AF? Im trying to be patient ( month 4 of ttc) but I'd be very grateful for any insight.

Thanks!

Michelle