PMDD! Please Help!

I think I might have PMDD and I wanted to get some advice from people who do on how to handle it.

I am dating this guy who I absolutely love. We’ve had a lot of issues in the past but Im doing my best to forgive and move on, because he matters more. Everything is great and I’m completely and totally happy for 2 weeks every month, but then that third week hits and I get really anxious and insecure about us, who I am, if we should still be together, whether he loves me - none of these things do I doubt regularly. And it will get worse and worse. I get horribly distraught and sad, beating myself up mentally and then him (also mentally). I’ll spend time trying to “wait it out” and then always convince myself we need to break up. At that point we get in a big fight, I spew my overthinking at him, he rationalizes with me, and then it’s all better for a bit until I start feeling the exact same way.

He’s as understanding as can be, but I’m worried he’s kinda tired of it, and honestly so am I.

I also sometimes get depressed (feel really heavy emotionally) and I have been experiencing insomnia too.

Does this sound like PMDD? How do I cope with something this extreme?

Thank you for your advice,

-Desperate and Hurting