I seriously thought I wrote this post for a moment!
I'm self diagnosed with PMDD and I do plan on going to a doctor, but I'm stupid and keep delaying it because of anxiety.
My SO and I would have massive fights every month or so. I'd become irrational, angry, irritable. I'd blame him for all of my problems and things about our relationship that I was normally OK with were suddenly huge problems. I was very depressed and sad in general during these times.
Eventually I made the connection, because it was getting bad and I knew I was acting crazy. I ended up realizing these moods were happening around my period, googled symptoms, and found out about PMDD like you did.
I've tried to manage it on my own for the past couple of years and I've done an OK job of managing it when it comes to my relationship, though it took awhile to understand myself.
Even after I realized it, there was still so many times I'd blow up and I would be so sure of why I was angry/sad. And then.. my period would come. I would feel like a fool and hang my head in defeat. I felt like every point I made just went out the window and I had made a big show for nothing.
But after some thought, I would realize the things that triggered my rage /were/ bothering me, but I was definitely blowing it out proportion and behaving irrationally. Now, I kind of make a mental list and reevaluate the situation when I'm thinking clearly to see if it's worth discussing with my SO.
I also try to track my period. I will give my SO a heads up when I know it is close and he tries to keep that in mind. I also try to keep to myself in general. I bite my tongue a lot - if I start getting pissed about something, I just do my best to stay calm and I tell myself it is NOT worth it. I tell myself it will pass, this is not who I am, remind myself of all the good things in my life, etc. I'll usually binge watch a show or something to keep my mind occupied and to pass time until I'm normal again.
I hope any of those tips help, and I'm sure going to the doctor is going to be a huge help in managing this.