Letrazole question.

So I took letrazole 2.5 MG for 5 days days 4 through 8 of my cyle to try to get me to ovulate sooner. It's now day 13 and no positive opk. I usually ovulate day 17 or 18 but only have 23 to 26 day cycles which is the problem. Anybody use letrazole out there and when did you ovulate? I'm afraid it's not working and they will have to up the dose next month which I really don't want. Baby dust to all!