OPK digital reading "high" for several days with no surge

This is my first month using an opk. I've been doing the Clear Blue Digital for 10 days now. Day 1 was negative, then everyday since then has been "high" but no surge has been detected. My period has been insanely irregular since going off the pill -- 28, then skipped a month, then 50 days, now due in a little over a week, so who knows when I actually ovulate, if at all. Has anyone else experienced this?