I'm not sure it's all diet, FWIW. Another aspect of the root chakra is money and survival...if you are anxious about these topics, that can impeded yer "flow"....I know for myself that when I'm worried about the bank balance I can delay my period by weeks if I'm not careful.
Those of us veg*n women who are very careful about our food and very empathetic towards animals [which I think you kind of HAVE to be, don't you think?] are devoting a lot of energy towards controlling what we buy and what we eat and how we live. Control isn't inherently a bad thing, but hanging on to abstract concepts prevents us from being grounded in our physical bodies [that downward energetic flow, again...in yogic physiology it's called "apana"...supposedly why you should not practice inverted yoga poses when menstruating. The PMS symptoms I experience are all too close to what happens when your energy just keeps going up and up and up and never lands...difficulty concentrating, binging on starchy foods, irritability, hard to GET to sleep and hard to wake up once asleep.
Once, in my callow youth, I was holding down a long-distance relationship and a vegan diet and my period wouldn't come and wouldn't come and I knew it wasn't because I was pregnant. I finally had too much red wine, freaked out, had a cheeseburger and slept with a friend of mine...and within hours, voila. Again, that is DEFINITELY not the recommended path but it was psychologically interesting.
Just a collection of random period thoughts....
Oh and send some grounding energy my way. I'd like the redcoats to start marching this week if possible.