What did you eat? Too many simple carbs with lead to an insulin spike, which will leave you feeling awful. Too much fiber took after not a lot of food will leave you with lots of gas, and stomach pains. Also, stay away from artificial sweeteners. Those bypass your digestion system all together and sit in the colon and ferment. That leads to gastrointestinal distress.
May I suggest some king salmon with a quinoa salad, served with a vinaigrette? That's a great meal for fat loss. Plus you'll feel full and it's some of the best tasting food on the planet.