Severe PMS, need help!

Lois • I like Gary Oldman and Tolkien
I'm 17, I've never really had this before but all of a sudden I've been hit with a wave of huge PMS. It's gotten to the point where I have insomnia, low sex drive, I'm constantly feeling down an ready and in some cases my anxiety levels are super high. My boyfriend is there for me every step and so is my mother, but I hate feeling this way. I hate doubting myself all the time, I hate feeling down about myself, it's seriously putting a strain on my college work, decisions for my future, my relationships, etc. It's like I only have 2 weeks in a month to myself where I feel sorta myself and human. Last month I got it real bad but with added nausea and anxiety, this is the second time but instead of nausea and anxiety, it's depression and tears. I'm also sleeping with my mum every night so I don't feel so alone. I'm going to visit a sexual health clinic and see what they say, but any suggestions on how to make myself feel better and prevent this from happening in the future? What do you think brought all this on? I think perhaps it was hormonal imbalance, but I'd love to hear and older persons perspective. Thank you x