What are you doing differently when you have the sore throat or cold? Are taking lots of vitamin C? You could be sensitive to the C... you could be taking too much.
Also, if it is food related and not supplement related, make sure to chew A LOT.... until your food is liquified. Also, it's best to drink most fluids a half hour before or after your meal. Try not to drink a bunch while you are eating. It's also important to sit and eat and make it a ritual.