You could easily get a negative at 8 - 9 days past IUI and test positive a few days later. At 8 - 9 days you wouldn't likely have much HCG in your system unless you had a trigger shot, and then the test really wouldn't tell you anything anyway.
I tested 10, 11, 12, 13, and 14 days after IUI. On days 10 and 11 it was so faint I wasn't sure (probably wouldn't have registered at all on days 8 and 9). On days 12 and 13 it was dark enough to believe, and on day 14 it was very clear. I also had my blood drawn on day 14, and it was off the chart high.
at 3:54 PM on Aug. 13, 2009