Seasonal depression

I have an overall blessed life. I have such a loving and caring family who always have my back and are always there for me. I get to go to school to pursue my dreams at the college I picked. I have a bed to sleep on in a lovely house in a good neighbor. I also am blessed to have three meals a day plus a dessert. I have a life some people might dream of having. I really don't have much to complain about. Why is at that I still find myself so sad and depressed. 

    During the same time of the year I find myself in this routine. I get up to go to school, come home and take a nap, wake up to take a shower, then go right back to sleep and repeat. I don't like to interact with any one. I get irritated over the smallest things. I stay in my room all the time watching tv, on my phone, or during school work. I cry myself to sleep without really having to cry. I sleep so much because I get to escape my reality. It can be the only time I am truly at peace. When ever I wake up I get so upset that I'm back. But I am not suicidal, I don't want to end my life. There are so many people that I love and care for that I could never do such a thing. Nor do I want to. So why is it that I find myself so depressed? Is because I have to much alone time? Is it because my life is stagnant? I don't know, but I always seem to snap out of it eventually. I guess it is what it is.