Endoscopy, colonoscopy done. Polyps removed 2 months ago, all beningn. Last week hgb results 12.8. Confused. What this could be?

Sounds normal. If your concern is a slightly low hemoglobin, 12.8 is still within normal range, and I am not sure you need to be very concerned. There are many benign causes of anemia, not related to the stomach or colon, like thalassemia. Questions for your doctor. What is causing my anemia? Is it iron deficiency? If it is iron deficiency, should I have a capsule endoscopy done since EGD/Colonoscopy normal?
Confused about... What? 12.8 is normal for hemoglobin. Was it much higher before, and dropped? That would be a concern, but not a 12.8 by itself.