I really do not understand why Susten is prescribed for you, and that too 200mg twice daily. Susten is given only in women likely to have / proven progesterone (luteal phase) deficiency. One rarely requires 300 mg per day. Usually it is 100 to 200 mg per day. If ovulation was documented, a pregnancy test can be done 14 days after documented ovulation - if negative, progesterone (Susten) should be stopped. You need to be examined to see possible cause of pain.