Frequent Anal Glad Expression

I have a goldendoodle who is a year and a half old. Since she was about six months we have had to had her anal glands expressed by the vet every month or so. Over the last two months she has been needing to have them expressed every two weeks. She has only ever been fed Canidae kibble with about a tablespoon of Merrick's "Puppy Plate" mixed in for her morning feeding, then boiled chicken mixed in for the evening feeding. We have tried not mixing anything in, but she will not eat if we don't. The vet has assured us that there is nothing wrong with having her anal glands expressed every two weeks but we are still concerned. Also, we've tried giving her pumpkin and raw carrots, but neither make a difference. Has anyone else had this experience? Is this really not all that uncommon or should we seek another opinion?