Is it possible to get a positive OPK and not ovulate?

My bbt this cycle is all kinds of screwed up anyways because for awhile I wasn't going to try and my sister was in an accident so I was out of town and not taking it and then I came back and my times haven't been super consistent so I'm not taking to much stock in it, But...

I got a positive opk on CD 13 after a dip on CD 11 or 12 and then the rise, but now it's going back down again even below my coverline which its never done before.

It has also been cold in our house the last two mornings and I've been sleeping without a shirt so that may have affected my body temperature.

It's just odd...