You have not mentioned what kind of surgery was performed on you. Most probably, a portion of your pancreas was removed. After this kind of surgery, the patient may develop poor absorption of food because of:
a) Deficiency of pancreatic enzymes
b) Poor mixing of pancreatic juice with food because of a change in the anatomy after the surgery.
You may need to take pancreatic enzymes and extra iron and vitamins (to improve your haemoglobin levels). I suggest you contact a gastroenterologist who will be able to provide you with the correct treatment plan.