What Does Severe Fluctuation In Hemoglobin Count Indicate?

Question: My mother is 73. Last year, she suddenly became severely anemic and was hospitilized and given several pints of blood. From April until July, her hemoglobin count continued to rise, reaching somewhere a little over 11. In July, it dropped to around 9, then started climbing again until the present. It has dropped to 8.4 on the last test. During all this she has had endoscopy, colonoscopy, and the pill cam. Pill cam determined a bleed in the blood vessels, which was immediately repaired. Visited gastroenterologist for follow-up just last month, and she said no need for further visits unless hemoglobin drops again. This month, here we are with it at 8.4.
Primary care doctor suggests seeing hematologist....I am wondering what kind of things could cause this? Please help, because it will be 90 days before her blood is tested again. I am worried about it dropping to an even more dangerous level, it was a low 4 when we took her to the ER last year. I am terrified it could be cancer, but none of the tests have shown anything so far. What kind of tests should I request?