This can be because of reappearance of Depression. What you can do here is start medicines. Once you feel comfortable, start physical exercise (Walking, jogging, cycling, Gym.. anything out of these) and mental exercise (Meditation, pranayams,relaxation practices etc) which will help you in increasing your stress fighting capacity and will lift up your mood naturally. After 3 months of exercises start reducing medicines gradually as per your doctor’s advice and maintain yourself on exercise. However, in some cases Depression may reappear as Depression is recurring disorder. In that case see your doctor again and do as per his advice.