If so...a new study may have the answer.
Researchers working in Australian have discovered that a symphony of hormonal signals and changes tell the body to slow metabolism and increase the urge to eat up to a year after weight loss.
According to Time Magazine:
"Many previous studies have shown that when overweight people slim down, their bodies respond vigorously, by undergoing changes in hormones that affect hunger and satiety — "multiple compensatory mechanisms encouraging weight gain," as the authors put it. For instance, when obese people lose body fat, levels of the hormone leptin, which is produced by fat cells, drop. That signals to the brain that the body's energy stores are low, slowing metabolism and triggering hunger."
The reason for this trigger? It was an evelotionary addaptation to help people survice, but in a word or abudant food it now has the exatct opposite effect.