Painting winter is only difficult because it is cold. It is no less inspirational. Think about it. The trees are bare so that you appreciate their true shape. The bark and lichens shine in the sun. Shadows are longer and make for interesting compositions. Cold air looks different than warm air as does winter sunlight. There are so many new things to depict when the leaves fall. Even water changes color. When snow falls, it transforms the landscape instantly, which also changes interior spaces based on what comes through the windows. People dressed in coats are a thing.
Winter is also a time to be quiet, meditate, read books, make soup. It is a good time to practice a new technique, study, visit museums. I like to do etching during the winter as it is an indoor activity. Most of my etchings are winter scenes. So as you struggle with the lack of light, remember that this time is important. Give yourself permission to relax. Enjoy the quiet and even be inspired by the changes that are taking place.