how can i fix my Vauxhall Corsa (C) 54 Central Locking?

for some reason my central locking has gone dodgy, when i press the unlock button on my keys it unlocks all the doors then whithin a split second it locks, unlocks and locks the doors again. I have been unlocking the car manuly but when i am driving it locks and unlocks itself.
its a vauxhall corsa 1.2 design 54 plate