PC cream can be used not only on breasts, while PM cream you apply only to your brests/chest area. So, you apply PM cream (your own dosage) on thighs, for example, or neck or lower back once a day, and PM cream as you usually do. I sometimes apply PC cream on breasts directly (was recommended by one of those doctors for breast enlargement, I gave the links in my program somewhere).
I was also wondering if I could use both at the same time. Of course there's no study done on the subject (surprise surprise). I was just trying to think - progesterone is imprtant for breast development as well as estrogen (actually, prolactine is too). One is responsible for fat storage in breast area and another one is for development of the lobes, ducts and so on. So in my opinion they are not conflicting but rather helping together. Don't quote me on that though
that's just my thinking out loud! 
Besides, PM cream doesn't have a systemic effect, it means it will not mess your hormonal balance by adding estrogen in luteal phase when progesterone should be high, not estrogen.
I was also wondering if I could use both at the same time. Of course there's no study done on the subject (surprise surprise). I was just trying to think - progesterone is imprtant for breast development as well as estrogen (actually, prolactine is too). One is responsible for fat storage in breast area and another one is for development of the lobes, ducts and so on. So in my opinion they are not conflicting but rather helping together. Don't quote me on that though
that's just my thinking out loud! Besides, PM cream doesn't have a systemic effect, it means it will not mess your hormonal balance by adding estrogen in luteal phase when progesterone should be high, not estrogen.