I was literally about to post this myself! Yes, it's started happening to me too and the reason is because my sinuses are blocked - but they're not "blocked" with anything, it feels like they're swollen/inflamed so I can't breathe through them which is making me have to breathe through my mouth. This has only started happening around the same time as all my other hormonal symptoms. Is it a known "thing" or do you think it's unconnected?!