Do be aware that not all GPs have the slightest idea about the treatment we're having (as I have personally discovered). She may be right as allergic reactions can happen when your body has decided that it's had enough of something after years of being exposed to it. However, she could just as easily be wrong so worth getting another opinion - particularly since it doesn't sound as if she even examined you properly. And if you are having an allergic reaction, you shouldn't just continue on without some sort of review.