No items in creative inventory (classic inventory), you can only use /give to give yourself command blocks.

I went to my world today, only to find there was nothing in my creative inventory! I did /give but it would only let me give myself command blocks! When I closed Minecraft and opened it again, it was just fine! I am very confused. (Just a note, my inventory was on classic edition) {Another note is that I play Minecraft Pocket Edition}