OPK - Something wrong?

Nicola
I'm new to this so I might be totally wrong. I'd had a little cramping and change in CM so decided to do OPK. My periods are v irregular so decided I needed cue. OPK came out positive (bottom of pic). Next evening I did the above one and it was completely negative! I BDd on day of surge and two days after. Do I still have a chance? Feel clueless! Xx