The core reason why medical advice online is "bad" is because it is not tailored to you as an individual. Even written descriptions of symptoms is only going to get you so far. Its still too generic and imprecise - you need personal data. Given this caveat, the advice of webmd, cdc, or mayo is going to be leagues better than YouTube, mostly because it will err on the side of caution, instead of recommending random supplements or mediocre exercise regimens.