All negative OPK

[Klee30]

I am on my 3rd cycle of clomid 100mg cd 2-6. I always use the answer brand opk and always get a positive on cd14 and the positives continue until I run out of sticks (i buy the 20 strip tests). I used a CVS pharmacy brand (7 strips) this cycle I started testing on cd11 and still no positive I got an ultrasound to check the folicles(sp?) on cd11 and my dr. said I would ovulate any day. Whats the deal???? Did I not ovulate this month even with the clomid?? Any one have the same problem and end up with a positive hpt????