What causes constant burping whether hungry or full during the day?

Burping. Burping probably a normal response- resulting in letting out of air by relaxing the esophageal sphincter. It may occur more frequently when you eat in a hurry, or use of carbonated beverages. When eat hurriedly you tend to swallow more air which has to be expelled. Frequent belching may also be due to acid reflux, hiatal hernia, peptic ulcer disease etc. These need to be addressed if excessive.