Weight management has so many factors. There are the obvious ones: diet and exercise.
Then there are the not so obvious. Medications such as antidepressants have weight gain as a side effect.
There are other medical reasons such as thyroid problems that can affect weight management.
Don't forget stress hormones. And sleep.
There is also the possibility that some foods may be making you sick. This can be from the food itself (allergies or intolerances) or from additives in processed foods or from pollutants...read on...
There are a few people out there that believe that pollutants in the enviroment can also have some effect. There is a recent article on how plastic can be making you fat...
Work with your doctor as well as a dietician to help you reach your target healthy weight.
