I went through this same thing with Ellie and once you get into a routine, it wil be much easier.
I didn't want to blindly trust the vet or internist either, so I look stuff up for myself (well okay, I read what Yorkieluv has to say and go from there
) because they may know how to medically manage these issues but I think for most vets, nutrition is a weak area...
I am not nearly strict enough with Ellie in my opinion and hopefully I don't regret it someday. But, along with liver issues, she can't have high fat because of her pancreas and I don't want her to constantly eat the same foods (although it happens anyway) because of her allergy/hypersensitivity issues.
I'm not having her nutritionist change her recipe because she is doing okay but if we need to change it for her GI issues, I think I will ask to switch to fish, egg and tofu.
Have you tried mixig yogurt with the kibble until you can talk to a nutritionist?
By the way, I have found that nutritionists don't seem to be nearly as concerned about things like red meat as we are. Ellie's nutritionist created her recipe so that I could swap out one meat for another and give variety. The same goes for carbs, oil and vegetables. That may be something you'd want your nutritionist to do so that if they don't agree about the low purine thing, you still have the vitamins, minerals and protein percentage right but can pick ingredients yourself.