Opks: How many negatives before positive


I've gotten 14 negative opks. I'm on CD 25 and still have not ovulated. Usually my cycles are around 34 to 38 days and occasionally I'll go as long as 45. Luteal phase is always 15 days. I'm thinking that's happening this time. I've been using an opk, sometimes 2 everyday for the past 14 days. How long have you all gone before you got your positive? What's the longest? What is the longest day of ovulation you have had?