If you look young and healthy, but complain of a wide array of symptoms, there are going to be people who will not believe you. From my experience and from what I have heard from other patients, some of these people will also make it their personal mission to tell other people that you are not as sick as you say you are.
The problem with this whole situation is, of course, that on your bad days when you are too sick to get out of bed or have to sit down in the shower, these people don’t get to see you. They only see you on the days when you feel well enough to go out and try to do things. One solution I have found to this is to make sure that I go to work or school on some of my bad days if it’s at all possible (and, of course, only if it’s safe). You only have to show up looking gaunt a few times before people change their perspective.
Beyond this, it is just something that I have learned to accept over time. In fact, the worst part is that I know that if this had not happened to me, I would not believe it either.