Certainly doesn't sound like cancer or anything, more like hormonal changes.
But, I'm not sure what you mean- so you missed your period, took one pregnancy test and it was positive, and you took another and it was negative?
If that's what happened, my guess is you probably are pregnant and the second test was a fluke (false negatives are more common than false positives) or perhaps you were pregnant and no longer are (this is common in early stages of pregnancies, not necessarily a miscarriage, some pregnancies just don't make it).
Or your cycle could just be all screwed up right now- which would explain the missed period, sore breasts, queasiness, etc.
Let me know what your gyno says!