Is it possible to never get a positive opk?

This is the first month I've used an opk. I started using it on day 9 of my cycle. I usually feel like I'm ovulating between day 11 and 12. I got pregnant in February using my own method but had a miscarriage. I had sex very early on day 9 because that was my only opportunity this month. I feel like I'm ovulating now (Day 12). I've been using an opk twice, sometimes even three times a day. They were all negative. The two that I took earlier today were close to being positive but then I took another one about 15 minutes ago and it was completely negative. What's the deal? The chances are already low because the sperm is 4 days old inside of me now. But I'm just wondering if it's possible to never get a positive opk, even when testing multiple times a day with undiluted (or mostly) urine?