No. This is not natural English and it would be a red flag to a native speaker. I kind of understand it, but it's not clear to me. I think it's saying that English was learned starting from the very first years of school, but "English medium" isn't ever used to express knowledge of the English language.

No, it's not, and I'm not sure what it means. Maybe, "I've studied English ever since I started it in school." ? or "I've studied English ever since (insert grade here) grade."

If you started learning right at the beginning of your scholastic career, you could say "Right from my earliest schooling, I've studied in English" but as it stands , it would not be correct English usage. this part "Right from my schooling" lacks a defining time. You could say "in an English medium" but just "in English medium" is not English usage. However, you can see that an English speaker can understand your communication. How is your spoken English ? I find that reading is completely different to conversing in a different language.