I used to have a 2 day LH surge every month for the past, well, more than a year that we've been ttc. Now all the sudden it's been a 3 day surge both last month and this month. Is there anyone who has experience with this? What changes the length of the surge? Is there a reason to be concerned? My o day has varied the past few months as well and it always used to be on the same day each cycle. I'm confused!