Bad Food

I just had two teas****s from a cup of their raspberry flavoured Nutriday yoghurt that expires on 02 April 2015 and it tasted very acidic like it had some chemical in it. I even asked a colleague to taste to make sure it was not my taste buds and she also had the same reaction. This worries me because I bought at least 6 of the 6 packs and I still have 3 (18 cups) left. The acidic/metallic taste just won't go away and it just keeps coming back up into my throat.