First you have to check your Height,So that you can know your ideal body weight as per your height.Accordingly you can ask for a Dietician to guide you which will help in keeping your weight check.
Tiredness could be due to improper diet,dietary supplements.You might have to take some High Protein low fat diet,less oil in your diet.
Avoid exerting too much.Can take some coconut water twice a week.
Next Steps
Consult a dietician.
Health Tips
If still Nausea persist,Meet a General Physician.As you might require few investigations.