No ovulation last month

Well... it was my first cycle on clomid 50mg days 5-9. Started testing with opks the day after my last pill until cd30. Glow kept pushing my estimated period out every negative ovulation day I recorded. So according to glow my period was due in 12 days from today but instead came today(cd33). Grr!! Has anyone not ovulated on clomid like this before? It's so frustrating hoping to get a positive opk day after day with only negatives in sight.... thoughts? Suggestions?