Why do I always feel left out and invisible in every social group?

I always end up being left out in every environment. I can’t seem to speak up when I’m around people. Everywhere I go, everyone is in a group, talking and laughing, while I don’t feel like I belong anywhere. I don’t talk, and I don’t laugh. Usually, someone has to ask me something first for me to answer.
When I try to start a conversation, my voice seems to go unheard, and it feels as if I’m asking meaningless questions. Sometimes people make remarks or tease me, and I can’t respond. Some cold-hearted and selfish people notice that I don’t stand up for myself and increase their teasing. I don’t know how to fit in with people or find my own path.
I have seen quiet people who speak very little, but for them it was their own choice. I want to talk, but either my voice won’t come out, or nobody listens.
Why do I always feel left out and invisible in every social group?
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