No Period, Not Pregnant

Anna
I've been on the pill for 8 years. My hubby and I want to have a baby, so I stopped taking the pill the day before my last period. Today is Cycle Day 34. I was expecting my period a week ago, and have taken 2 pregnancy tests, so I know I'm not pregnant. I guess I just wanted to know, how do you use the ovulation kits if you can't estimate the 'middle' of your cycle?  I've read you can have irregular periods after coming off the pill... If I don't get my period, how can I use Glow to guess the best time to pee on the ovulation stick? Glow was so helpful before, telling me the dates and stats for each day, but I feel really lost now that I have to keep moving my period due date back.