Positive pregnancy test, neg opk

So my periods are really irregular which means I take opks throughout my cycle. So on my previous pregnancy the opk was positive for days so I took a pregnancy test and it came back positive. This time my opks are negative but my pregnancy test is positive. I have no idea how far along I am due to how irregular my periods are. I'm just wondering if its normal for an opk to be negative even if you're pregnant considering they can't tell the difference between the two hormones?