I might be wrong, but what I know about OPKs is that once you've got a positive you shouldn't test again. This is because afterwards your body can be all over the place so getting a positive or a negative doesn't mean as such. A positive could also mean that you failed to ovulate the first time, and your body is trying again. Without having the OPKs in the middle, though, I would think that it is hard to pinpoint which of these things is occurring.