I can't find any ore... Diamonds, no, gold, no. Is there a specific biome..

No

There is no specific biome to search for ores under. However, some ores are especially uncommon and have depth requirements. Diamond and gold must be found deep, deep under ground, as in closer to bedrock (the dark grayish stuff at the bottom of the world unbreakable except in creative mode) than the surface. Also, except in creative mode one cannot break ores or even plain stone without the use of a pickaxe. Either an iron or diamond pickaxe is required for gold and other truly valuable ores.
In essence:
Check you are deep underground
Check you have a good pickaxe
Hope this helps!

There is no specific biome to search for ores under. However, some ores are especially uncommon and have depth requirements. Diamond and gold must be found deep, deep under ground, as in closer to bedrock (the dark grayish stuff at the bottom of the world unbreakable except in creative mode) than the surface. Also, except in creative mode one cannot break ores or even plain stone without the use of a pickaxe. Either an iron or diamond pickaxe is required for gold and other truly valuable ores.
In essence:
Check you are deep underground
Check you have a good pickaxe
Don't give up, ores are hard to find!
Tip: Don't just plunge down there and start digging random tunnels or you will become hopelessly lost and not find the way back up. Have a strategy for how you want to dig.
Tip: You cannot mine redstone. With anything. Don't try unless you feel you have to get it out of the way.
Warning: Keep your mine well lit or it will become infested with Monsters.
Warning: Don't dig straight up. If gravel is above you you will suffocate to death. Same with sand if you are near the surface underneath some sand. Take a couple of steps back before digging.

As far as I know, ores don't spawn specifically in different biomes. In older MCPE worlds, there was a bug where there were almost no ores. Maybe try to create a new world.