How long are you supposed to get positive opks

Joslyn

In an effort to avoid metformin which made me sick, I tried the soy isoflavones this cycle. I finally got a positive opk. But now it’s going on the 2nd day of positives (testing when I wake up and before bed). I normally get one positive then it’s gone in like 12 hours. I read that the soy can sometimes mess with your cycle. Is that what’s happening here or am I just finally ovulating normally so it looks different than it did before the soy?