Progesterone Suppositories and Testing??

Do Progesterone suppositories affect the results of a progesterone test?

Are you supposed to start taking progesterone suppositories AFTER you know you've ovulated?  

Can taking progesterone too early delay/prevent ovulation?

I have been TTC for approx. 1 year.  (Secondary infertility.  One previous miscarriage and one beautiful daughter.  Never had trouble conceiving the first two times.) My luteal phase this time around is around 8-10 days, which I believe is definitely on the short side.  (LPD?) This cycle I started on Clomid (50mg) days 5-9 and was told to take progesterone suppositories days 14-28.  I am now on cycle day 24.   Each month of TTC I have used OPK's and received a positive result every month around day 16 or 17.  This month I never received a positive result.  (I waited the required 3 days after my last Clomid pill before testing with the OPK so I did not mess with any results.)

My doctors assistant called today to say that my progesterone blood test (done on day 21) indicated that I had ovulated a week prior.  (Level was 84.1 - not sure what that means, but am told it is high.)  I explained that I did not get a positive OPK this month and she seemed surprised.  She was unable to answer the questions I asked and I have to wait until my next dr. appt to address them with the doctor directly... which isn't supposed to be for another 2 months.  

I have also been reading and it looks like most women taking progesterone start it once they know they have ovulated.  My doctor told me to start on day 14 and never mentioned about waiting to ovulate?  

Your comments/answers are appreciated!