The reason you've heard that progesterone could be the problem is that when the egg is fertilized the body naturally keeps producing progesterone. In a normal cycle, at the time of ovulation, progesterone is at its peak....If conception does not occur it begins to drop. Progesterone helps to maintain the pregnancy. So, your answer is 'no', taking natural progesterone cream will not be a problem. However, I would ask your doctor to run your hormone levels at or around peak time to see if you are low on progesterone. Generally, if a woman conceives, and progesterone is low, she will begin to spot. Then, sometimes a shot of progesterone is required. If you use progesterone cream, it is not necessary, as a rule, to use it during your period.