When no one notices your pain

I need your opinion and advice if possible. I'm in senior year of high school. I am shy and introvert. I have no friends, I had some back in middle and primary school, I also was the "fulfilling friend" to someone all middle school long. There are only three people in my class whom I talk to quite regularly and openly. We laugh, we talk, we hang out together only at school. Otherwise, the rest of the class likes me. They tell me I'm nice, kind and intelligent. As I laugh pretty easily, they often come at me to tell me jokes. I'm always laughing -- could be how I hide my sadness?When they talk a bit with me, I don't really know how to answer but I still do. But I don't feel like they want to hang with me. I doubt they're waiting for me to come to them as they know how shy I am, I've known them for more than a year now. I know I am shy and quiet and people don't like such persons very much.I am not so well integrated to the class. Last time we were discussing the fact why one of our classmates wasn't liked by the entire class, they said she was the only one not integrated. I am more than her, yes, but I'm still very very shy talking to all of the other people in my class. Can't they see? Each week, when asking about what we've done during the weekend I always say nothing. Because I don't do anything on weekends. I have no friends to go out with! Don't they understand? When we were talking about New Year"s Eve plans, my friend asked me if I couldn't ask my friends to plan something. I remained quiet. I admit to myself that I have no friends, I want them to know but still I can't find the courage to admit it to others. Do my classmates actually think I have friends outside of school? ... I feel rejected. For instance,me and two of my friends (don't know if I should call them that still) were discussing eating plans. One said she was going to eat at a guy's home and the other said she was going to eat outside with another guy. I heard them because I was next to one of them. I felt pretty bad: ending up alone as usual, no one asking me to come with them. I just feel like a ghost in class. If they need me they'll talk to me, if they're in a good mood they'll tell me a good joke, otherwise they'll just ignore me. I'm never the one people want to have serious conversations with. Never the one people talk about when I'm not here.These I understand I should make the first step but I feel worthless. I know I've often been alone, but it doesn't mean I enjoy it. I remain unnoticed. I've had a rough month, feeling very lonely and overwhelmed by my family problems (no one to talk about it with) , but no one noticed that I'm in total despair. I wish I was able to break down in front of them all so that they would finally see my pain. I'm so used to answering "I'm fine thanks and you?" but people don't care. Don't they see I'm hiding so much behind my constant laughters in class? I am exhausted.I feel so unhappy. I know I've always been invisible but I still wish they would notice me... Do you understand?