Can you get an positive OPK and then not actually ovulate?

Or if you get the SURGE line that means you are DEFINITELY going to ovulate within 12-36 hours after that??? I am wondering bc I had the surge and did the BD etc and my period isn't here yet but early preg test says BFN. I have had 2 cysts while using Clomid but haven't used it for 2 months (it CAUSED the cysts). I have never had cysts before Clomid.