The cold weather, lack of lights and abuse of heater probably contributes of our lack of energy and don't help us to be energetic, ready to get up and start the day when is all dark outside.
Here in London, its pretty bad considering that we have got 7 months of greyness, cold, wind and endless rain versus 4 months of uncertain weather mitigated between sun and rain. Anyhow, London is not a city made to be 30 degrees anyway it'd be unbearable if it was the case.
Although we are in March now and i can finally see lights at the end of the winter tunnel. At the end of the month we will be changing hours and we could stated winter behind us. Woooop.
What i am trying to say is making a good thing of a bad thing and don't let the weather affects our mood and energy. Indeed, we should be more focus into things that we can control as our alimentation and lifestyle choices to make the best of it.
Having a good quality sleep is essential as a lack can issue of a weight gain which result of being more tired and hungry which outcome of gaining even more weight — Its a vicious cycle.
Take into consideration your alimentation and lifestyle and break this cycle — Food is our energy source.
Please avoid prohibits processed food and remember that natural knows best! What you need is vitamins C (natural one as peppers, kiwi, mango, orange etc and/or supplement of vitamins my favourite are "haliborange" from boots they really give you a boost), vitamins B (eggs, nuts, whole-grains) and folic acid (as green vegetables, lentils, fruits, rice or soya milk, sunflower seeds).
Raw vegetables and fruits are much better than cooked (avoid fried) as a large percentage of nutriments and vitamins reduced in baking.
Your sensitivity to certain food may be another reason of your tiredness, exposing your system to certain aliment and chemicals may blown your body (for example intolerance to lactose).
Having too much refined carbs (quick sugar) in one go wont be good for you rather go for complex carbs (low sugar) which will be a much clever choice by bringing you high fibre and protein which is the energy your body needs.