Not sure if this helps but when I wasn't taking my progesterone continuously (and thought breaks were better) I would feel dreadful for the first week of stopping, then a bit better the next week and then amazing for the next 2 weeks and then awful again, so would go back on it. This sounds a bit like your pattern!
I figured out that when you first start it you feel good, then after a few days it can make me feel a bit ramped up (my endocrinologist told me it was dormant oestrogen receptors becoming active again - which may not apply to you if you take oestrogen?). Then when I stopped it I would get withdrawal on top of all the active oestrogen receptors. Then after 2 weeks, the receptors would dumb back down and I would be full up with the progesterone (as it builds up and hangs about for a while) without all the ramping up.
Now I just take continuously I've got over the ramping up and my oestrogen surges are much better controlled, so anxiety, burning hot skin and migraines have gone. It's the first time I've not felt sick for 2 months straight!
Re. cancer, I thought that progesterone doesn't directly cause cancer as even the synthetic Norethisterone is used to treat it and that the small risk was about oestrogen being controlled (dominated) enough by progesterone to keep cancer at bay vs those who take oestrogen only HRT because they don't have to worry about the lining building up. If it was about breast cancer though I don't know but hope it's not a risk as I'm taking it because my crazy oestrogen surges caused liver growths and didn't want any breast issues too.
I remember the wording of those studies being really unclear though!