Victoria, you have found the heart of the problem. He doesn't believe you're sick. It's ridiculous he won't take your word for it - if you had a fever, were coughing, bleeding, etc, it would be so easy to prove but fatigue is hard for the external observer to measure.
You must have an annual exam with a western doctor, right? Schedule one now and bring him. Let him hear from an "authority figure" exactly what your health constraints are.
Is there a support group out there for your particular condition? Perhaps those people would have better advice on how to explain it to someone who just doesn't get it.
I have to admit that I have been on the other side of the scenario where I didn't quite understand someone's health-based requirements, because I've (knock on wood) been lucky enough to enjoy robust health/strength and don't have a relevant experience to draw on. Even if someone says "I have this issue", I don't know that it means "x and y and z". While most people would make the mental leap to "x and y and z" on their own, I wouldn't be capable of doing so. Once the person explicitly explains "x and y and z" to me, and doesn't expect me to make the mental leap, then I know how to behave appropriately. It sounds like you have already done a good job of explaining everything in detail to your husband, but maybe he just hasn't heard the one thing that would make it click for him.