medline plus is a great site , very informative .I use it and it's helped me when I had to go to the doctor, I had some ideas and information and was better prepared for my visit .
webmd.com has a symptom diagnosis, its like a body, and you click the part or symptoms, and it calculates all the possible diagnosis' after asking a few questions, you can narrow it down to a couple.
wrongdiagnosis.com is a great site. you can type in individual symptoms and get matches to diseases or even put multiple symptoms into a search and it will bring back all possible diseases related.
Good luck. I hope you find what you are looking for.
webmd.com symptom checker