You may have not eaten a regular diet during your fever & cold from last few days, hence you might have lost some weight.Now that you feel ok, have a balanced and a healthy diet with chapati, vegetable, rice & dal, salad and may be a sweetdish after meals to gain back the weight lost. Also try to eat small snacks after every 2-3 hours. Have fresh fruits two times a day. Snacks can include peanuts, dhokla, aloo or cheese sandwiches, dry fruits like kaju, kismis, dahiwada, idlis, upma, poha etc.