I need help

Hello. Does anyone know how to rebuild self-confidence when everything just seems to be falling apart? I was once a flourishing student back in primary up to middle school. I was never scared of speaking in front of crowds and even participated in competitions that involved public speaking. However, my confidence suddenly started to drop during 9th grade. For some reason, I now start to feel easily overwhelmed when approaching people, especially in presenting and participating in class (I am even second guessing whether I should post this or not as I type). I am in 12th grade now and I do not think I have made any major improvements so far, in fact, I feel like I'm getting worse and worse. I know that I am going through issues that contributes to the way I am. However, to overcome my problems, I thought it would be helpful if I could first build my self-esteem and lessen my self-doubt. Unfortunately, I do not know how to and watching motivational videos and tutorials does not seem to help.

(Pardon my grammatical errors. English is not my first language.)