You probably feel this way because if you cut junk food out completely and suddenly, your body is shocked by the sudden change. Also, junk food has a lot of sugar, which can make you feel energetic, so when you cut junk food out right away your body isn't used to not getting the sugar you used to consume. My advice is to take baby steps. Cut out candy/ice cream, then chips, then soda. etc. until you are consuming less or none at all.
Add a cup of low-fat milk, a part-skim mozzarella stick, or a half cup of low-sodium cottage cheese to breakfast, and you may have a belly-busting win. While lots of research links calcium with lower body weights, results from a 2014 study suggest that calcium-containing foods may reduce waist circumference in those genetically predisposed to carrying weight in their midsection.