What Causes Excessive Weight Gain After A Gastric Bypass Surgery?

Hello, I had a gastric bypass about 12 years ago and lost approx 150 lbs. I have, over the last 4-6 years, gained 100 of it back. 4 years ago, I was diagnosed with colon cancer (stage 4) that matastisized to my liver... I have been through 2 surgeries and many rounds of chemo and radiation and have been in remission now for just over 2 years!! Anyway, my question... I have kept eating records for my diatician and she has said they look really good (as far as what I eat and the quantities that I eat) but, Im still gaining the weight. A few months ago I happened across an article for yeast overgrowth... I have about 3/4 of the symtoms. Fatigue, VERY achy joints, bloating and itchy areas on my body that I have always treated with a prescription from my Dr. I just had my yearly colonoscopy and in the report it says I had a lot of mucosal staining with a thick bile coating ... is this a yeast type of thing? Could it be why my gastric bypass is no longer passing food through my system as fast as it did a few years back and why I may be gaining my weight back? Any ideas or help would be great! Thanks for your time! :)