Hopefully you know by now not to trust everything you read online. This is ESPECIALLY true for medical information. There are many reasons online health information might not be reliable: The author is not a qualified medical professional, the information might be published by an entity with a vested interest in promoting something (think drug companies that might stand to make a profit), or there might be a disregard of scientific info in order to further an agenda (think of the link between autism and vaccines; science has proven there isn't a link yet some sites continue to perpetuate misinformation)
For these reasons using the TOECAP criteria (Trustworthy, Objective, Enough, Current, Accurate, Purpose) to evaluate your sources is very important. You can also use a combination of the sources listed on this libguide. DO NOT just rely on WebMD. Why should you not believe everything on WebMD? Read this article from the New York Times Magazine: A Prescription for Fear.