Is it possible to have dyslexia, dyscalculia, and dysgraphia?

Absolutely. One can have many learning disabilities. Your writing here seems to cogent and ok for middle school. As above me states, have your parents request testing at your school, in writing. They have 30 days to comply. Learning disabilities should have been evident at an earlier age, but go ahead and request essment. Good luck and do not give up!