wow, this is a complex array of requirements to meet, but i can assure you your dietitian should be able to sort you out just fine with a vegan diet that meets all those: if unsympathetic, find another one. That is pretty important.
So with PCOS you will need to be eating a high protein, low carbohydrate and a low glycemic diet. No soya or rice is fine, just you will need to be more prepared to cook for yourself at home, often from scratch. Many of the processed vegan protein 'replacements' are soya based. Make sure you eat plenty of protein dense foods that where possible are also nutrient dense:
nuts (introduce slowly since you seem to be quite allergy prone), seeds (particularly flax, hemp), wheat-based protein (i.e. seitan/wheat gluten), lentils, beans etc.
The important thing is to ensure a constant blood sugar level that avoids the peaks and troughs of a highly refined sugar diet. Make sure you include a real variety of wholegrains, varying day to day if possible. Pearled barley is particularly good for a cheap, low GI carbohydrate. Oats are particularly excellent, especially since the soluble fibre will help with cardiovascular health. I agree with emm7 that rice milk is usually very un-allergenic: perhaps you have a high sugar variety that is disagreeing with you? Hemp milk is great, but expensive, but there are plenty of others to try: almond milk (there is a type sweetened with agave syrup which is a great low GI refined sugar alternative), quinoa milk (personally don't like but worth a try), oat milk etc.
Vegetables will be resoundingly your lifeline. Variety is key! Green leafy vegetables will give you the best nutritional profile, in general, but also include lots of brightly coloured veggies like peppers, tomatoes, carrots, sweet potatoes and so on. Sweet potatoes and other sweet vegetables are a great way of eating unrefined sugars without feeling like you are missing out too much but, be aware that some can raise your blood sugar more than others quite rapidly and so should be moderated, to some extent. This also goes for fruits like cantaloupe and water melon, along with most dried fruit. Veggies wise, eat cautiously parsnips, plantain, potatoes (except boiled new), swede, turnip and yams. Go easy with corn, pumpkin, squash and sweet potato, though they are not so bad.
Fruits-wise, don't worry too much, but be careful that you don't eat fruit all day long to satisfy the sugar craving. Fruits are high in fructose and sugars that will sometimes rise your insulin levels much like any other refined source. Eat plentifully but with some moderation and stick to fruits like cherries, plums, grapefruits, peaches, apples and pears rather than the very sweet fruits like mango, pineapple, dates and so on. Dried apricots are apparently quite low GI.
That is all a big long winded, but I think I have just over-emphasised what would be resolutely given in a GI-diet table of low and high GI foods. It would then be a case of missing out what you are allergic to, what is meat or dairy based, and then eating the best variety of low GI foods wherever possible, from whatever is left.
Don't feel constrained: seek out your new diet with positivity, as if it were a medicine!
hope that helps
When others asked the truth of me, I was convinced it was not the truth they wanted, but an illusion they could bear to live with. Anais Nin