Why am i so sad every night?

I am 15 years old and ever since december i have been feeling kinda happy during the day but usually when i get home i feel sad and bored and dont want to play my games or do anything. Most of the time I just start crying for no apparent reason. I have not had anything horrible happen to me or family members or friends. I dont know what to do. I havnt told my parents anything because they might think im a baby for something. Please someone tell me whats going on and what to do,