Hi Rasputin
My Border is the same. She is very fussy about her food but normally will eat a meal a day, longest she has gone is three day. My vet also said not to worry as very common for the breed apparently.
I also just looked up
paroxysmal gluten-sensitive dyskinesia
, its actually what my dog went to the vets for 4 weeks ago as every 5 or 6 weeks she was walking around with very tensed back and stomach muscles. She also had extremely loud gurgles and noises from her stomach. The vet told me not to give here ANY food with wheat in it or cheap crappy biscuits that contain it....her favourite was gravy bones which are a prime culprit for this.
The trouble is if you look at the pack of just about every pet shop feed for dogs the have dire ingredients. If you look at most foods it is the first three ingredients that will normally tell you the quality of the product. The three to look out for which are bad for dogs are ...No cereal, No Meat meal and No animal derivatives or by products...What ever the latter three are! Another ploy the feed makers use is wording such as 'chicken meal' as opposed to chicken, clever wording for cheap products.
Any food should have a high genuine meat product.
I tried raw but she wouldn't eat it and she also contracted Campylobacter and E Coli, all in one it which really knocked her for six.
These links will give you excellent advice and let you know the foods.
Dog Food Reviews and Ratings | Dog Food Advisor — Dog Food Reviews and Ratings and
https://www.allaboutdogfood.co.uk/
My partner did a lot research about foods as we needed to get everything right for my dog. Our only mistake was to find a good food but we neglected to stop the gravy bone treats, now they have been removed all seems well.
It could be the same with your dog.
Hope all goes well.