The fortune enchantment's doesen't work

First thing when i got the fortune 3 enchantment book used it on my pickaxe and when i got to my strip mine i waited for the chunk of diamond ores that i waited for because i would enchant my pickaxe first before i mine the whole thing and then when i did about the amount that it gave me was exact number of ore's (the ores was eight blocks) yeah exact 8 also tested it on other ores such as coal and lapis also the exact number as amount of blocks was there.