I think i have Sunlight deficiency?

I live in Geneva Sitzerland and it's winter at the moment and always overcast and cloudy or snowing. I've feen feeling a bit flat sometimes recently and worried that these feelings could be cause by vitamin D deficiency, i haven't really been in the sunlight for about 2-3 weeks. I'm actaully from Australia so am used to being in the sun all day everyday. Please help!