I agree GP or they can refer you to a specialist Gyny who knows more about the matter. I eventually went direct to a private Gyny as not happy with family doctor's methods and it did the trick.
In the meantime....If you're a mess during that week I suggest take a self-care break for those 7 days, eg sunbath, read, walk, as you're distressing both yourself and clients and it's really unfair to use them as scapegoats. It's unprofessional to charge clients when you're not capable. My friend put herself in isolation during her PMS as she was a hateful, spiteful cow and came back her usual lovely sweet self when it passed.
From what you say you're not very productive during that time anyway so better to pamper yourself a bit so you're fit to rock.