I find that it is a bad idea to tell the doctor that you've looked up the symptoms on the internet - the self-diagnosis gets poo-pooed. And once, in the days before the internet, I went to a doctor and told him I had cystitis. When he asked "and what makes you think you have cystitis" (not nicely, I might add), I explained my symptoms, then he huffily wrote me a prescription for the correct antibiotics to treat cystitis. Nowadays I find the best way is just to describe the symptoms of whatever and let the doctor tell me what is wrong, even if I already know.