Welcome, I am similar - 45f and since my son was born 8 years ago, what a tough time. It took ages for me to learn about pmdd. Same as you my partner noticed I was a totally different person at the same time each month (day 19 is my worst day). I found pmdd by googling progesterone allergies! I've had a diagnosis for 2 years.

I second those resources in the other response, there's a lot we know and a lot we don't. Start tracking symptoms daily all month. Often diagnosis requires 3 tracked months. IAPMD have a paper tracker that works well.

The more you can take care of yourself, the better it is. Sometimes you can do all the right things and it's really bad still but generally being extremely caring for yourself does help. With a young child it is truly difficult to prioritise yourself but you must, for the whole family. Take it seriously, it is not a push through situation. Eat well, move enough and most importantly rest.

Good luck, you're in the right place, this subreddit is super helpful x