Clomid + Follicle scan + opk

Hi all,

I started with first cycle of clomid this month. Per my cycle, I got positive opk on CD13, however in the folicle scan on CD14, the egg size was only 1.1 cm (ofcourse which is already a bit off). I got a negative opk on CD14 and the Test line becoming lighter and lighter.

We went back again on CD19 (today) for follicle scan and the egg size was 1.8 cm and good lining. The doctor advise to do the deed in the next two days. Again, when tested with opk, it was negative.

Some history - last month when the doctor did follicle scan on CD14 and CD18, she said the egg wasn't growing properly and hence she started me with clomid from CD3-CD7 this cycle.

Question: is it possible that ovulation will happen in next 24-48 hours, but still the opk would be negative?

Would appreciate any response. Thanks in advance.