First make sure you are sleeping enough.
Is your nutrition sufficient? In general women need at least 1200 calories per day and men 1500.
Avoid monotony: a varied diet will be more likely to provide the nutritive elements you need to conserve your energy.
The sensation of fatigue may be stress-related, especially when you experience emotional stress. Do you feel tense at work or at home?
Lastly, don’t neglect physical exercise. Tired or not, get out in the fresh air every day. Walking is the minimum effort necessary for staying in shape.