Had to do some serious digging to find this thread on the internet. I've had this problem. First girl I went down on wasn't all that clean (few years ago, my standards were a little low =/ ) caused me to get the exact same sore throat symptoms every time. If I made damn well sure I swallowed nothing and used mouthwash I was fine. It got so bad once though that my throat was fucked up for 2 weeks and I started coughing up pleghm that, you guessed it, was brown and smelled like yeast. I was pretty grossed out.
Fast forwarding now, my current girlfriend causes the same problem only when I go down on her and she is the cleanest person I now know. We've been trying to figure out what exactly is causing the problem and it could simply be the soap she is using to clean herself before we have sex. Thanks for sharing your experience man, as shitty as it way, it's helped me out here 5 years later lol.