Unfortunately what I did might not be of help for anyone with the same problem. But here it goes:
Like I said, I was on 4.2.2 originally. But since I couldn't find a 4.2.2 official firmware, I had to download a 4.3 stock one. I flashed it once -- still the same problem. Tried flashing another ROM -- still the same problem. BUT THEN, I flashed the 4.3 stock ROM again, and it just worked! IDK what happened.
Anyways, hope someone can get the same results as me!