Let's see, where to start....
It is possible that you missed your O, but if you are having cramps, you might not have O'd yet. This cycle, I didn't get a + OPK as a matter of fact, they kept getting lighter. I went to have my progesterone checked and found out that my pain was O pain ON BOTH SIDES!

I did a generic OPK that evening for giggles and then it finally came up.
The flip side of that is the hot flashes and fatigue are also signs of pregnancy....so maybe you O'd and it missed the window during the tests. I also had hot flashes and moodiness with the Clomid, enough so that I have to take extra Zoloft on 'Clomid days' if I wouldn't have gotten my + this cycle.
Are you on the Clomid to try to help regulate your cycles? Or would maybe b/c be in order to throw it back in line?
Just throwing ideas out, hope it helped.