Progesterone Vaginal tablet(pregnone) - need help.... Confused.....

Hello Ladies,
I usually have irregular cycles but every month. Could not predict the date alone.Last cycle was 40 days. I went to the doc. She asked me to get the scan and blood report on 15th day.

Reports are normal except that i have low progesterone levels.
I am sure i ovulated on 15th day since i could find the discharge ( egg white and appropriate consistency). I also had cramps.
Doc has suggested me to use vaginal progesterone tablets along with few vits.
She has also asked us to be together while using the tablet for 10 days.

My question is:
If i ovulate on cd15, should i take this tab till cd26 and have IC... I had IC on cd15, 16, 17 and 18. Should it still be continued? isn't that a risk?.. cos if i have concieved wont that interrupt?

Confused.. pls help...