Unfortunately, the only way to know what food caused your food poisoning would be if the sickness came immediately after the last thing that you ate. If the sickness came after an extended period, there is no way of knowing what caused it.
It can take up to 48 hours after eating a contaminated food for the first symptoms to occur, which makes it hard to determine exactly what made you sick. Unless someone else ate them with you and is also sick, it's hard be 100% sure, unless you eat them again and the same thing happens.
It is very unlikely that blueberries caused the food poisoning. Rarely have fruits caused food poisoning unless they have been contaminated by an outside source.