The challenge for you is that you need a quick fix for a lifetime of being shy and fearful. You could speak to your teacher(s). At best, you will have sympathetic ones that will understand and probably suggest Toastmasters if they are aware of it and it is available locally. At worst, you will insensitive ones who say “suck it up buttercup!”
Reducing shyness, overcoming fear of public speaking and becoming good at it as well as raising your self-esteem don’t have quick fixes though. They require quite a bit of personal work, that takes time.
My suggestion would be to work on raising your self-esteem first. I would suggest going to the library, more than likely a public library vs the school library and look for books on raising one’s self-esteem. It can be as simple as incorporating positive self-talk into a daily habit. I can relate to low self-esteem growing up as my father was quite insulting to me on a daily basis. One of the techniques is to attempt to validate what others say and if it isn’t true, dispose of it.
When you start believing in yourself, your self-esteem will rise incrementally. I find it helpful to take a piece of paper and draw a T graph. On one side of the paper label it My Strengths. The other side My Weaknesses. The Weaknesses side will likely be easier to complete as those are the ones that others seem to keep telling us about and we believe. They aren’t necessarily true though. I would suggest that you filter your list of Weaknesses to only items that you know to be true. You state in your opening comments that you are afraid to tell anyone because they will think you to be dumb. The weakness is that you are afraid, not that you are dumb. That is a label that others may put on you.
Once you have completed this task, the next step is to focus on your strengths. This is the area that helps raise your self-esteem. The items on this side of the list can be good to draw from for daily self- affirmations. E.g., “I am good at …” “People seem to like it when I …”
Joining a Toastmasters club has been suggested if it is available to you. Many colleges & universities have a club in place. There are likely numerous students such as you that suffer in silence with the same problems. Toastmasters can help you find your voice. The challenge for students is fitting participation at a club meeting into what is likely an already heavy schedule. I can say from experience that the time you invest in attending and participating in a Toastmasters club will have more far-reaching, life-long positive effects than any other educational course you will take during your studies.
One last thought before I conclude, it occurs to me that perhaps your school has a mentoring or peer support program in place to help people going through the exact problems that you are. So maybe there would be value in talking to a teacher or perhaps a Guidance/Career Councilor.
Thanks for the question and good luck in your personal journey, where ever it may take you.