Thanks to you both for replying.

I was hoping OBmom would have an explanation for me. So you reckon this increase in respiratory frequency can be attributed also to progesterone pessaries, not just progesterone increasing naturally in the body during pregnancy?
In any case, the progesterone seems to have been doing its job in the week I've been on them. I had an appointment with the doctor today and his exact words were "I'm getting less and less worried about your pregnancy". Those are very encouraging words to hear. Cervix looking stable and lengthened. Very grateful for this movement in the right direction.
Hoping for good luck and great progress for everyone else too. <3
Charlotte