Do you mean -ve as in no line at all, or a line fainter than the test line on the opk?
I finished my first round of clomid about 4-5 days ago and am experiencing ovulation pains and cramping. My opk was -ve with a very faint line yesterday but definitely much darker today although not as dark as test line. So although its still a -ve, its obvious I'm gearing up for ovulation.
Are you getting the same?