I'm so glad you're doing so much volunteer work and that you're currently involved in three programs! Not only are you benefitting the community around you, but that will help you gain leadership skills and make you very competitive in your future applications and resumes.
To find volunteer opportunities for people16 and under, I would suggest reaching out to whatever your nearest volunteer center is. They should be able to tell you what nearby nonprofits have volunteer opportunities available to people in your age group.
Some common volunteer opportunities for those 16 and under include:
-Food Pantry help
-Clean Ups (such as at your local park or green initiative)
-Volunteer Opportunities your parent does with you.
-Volunteer opportunities where you'd be participating in activities such as arts and crafts at nonprofits that serve younger children.
If you don't have a local volunteer center that can help you, I would reach out to either local nonprofits that you think might offer some of the examples I gave or reach out to an adult who is involved in volunteer service who might know someone that can help you.
Hope this helps!