11DPO Negative Test, what do you think?

I normall have 36-38 day cycles, but this month, I started taking clomid. I ovulated on Feb 4th, (confirmed by bloodwork) so today makes 11DPO. i tested today for the first time, and it says Negative. I was at CD18 when I ovulated, so could it habe just been too soon? I was put on clomid to shorten my cycles. When should I test again?