Hi, Try adding oil pulling to the regime, it is great for any infections especially in or around mouth, throat area... edible clay may help with the detox.
I don't think there are many side effects of taking too much vitamin C apart for digestive issues, so maybe your body just needs some extra support to deal with the infection, apart for Vit C.
I love lipo-spheric C and started making my own, but also buy it whenever i can. It is great stuff.