Uh... wow! Sorry to be so harsh, but your husband sounds like an insensitive jerk! All that you do, PLUS a part time job, PLUS school, PLUS a chronic illness... just WOW!
To answer your question, when I worked at home, everybody assumed it was so easy, which made it harder. People called me at all hours of the day, people wanted me to do things or watch their kids just because I was home. What part of WORKING did they not understand? This is why I prefer working in the office, because people respect my time, so I can get more done. And honestly, working in an office is like a VACATION compared to all the responsibilities that wait for me at home.
I've done it all- I've done that WAH thing, I've done the part-time thing, I've done the SAHM thing, and I've worked outside the home. The easiest, BY FAR, is working outside the home.
But to me, the real issue, rather than justifying to your husband what you do in a day, is that he needs to man up and provide for his family in more ways than just bringing home the bacon. How can you communicate that to him? Stop doing everything for him. Just stop. You're not superwoman, you can't (AND SHOULDN'T) do it ALL. We have partners in life for a reason.
And from my heart to yours, with complete and utter sincerity, your husband should be so lucky to have a woman like you who takes on so much and is so giving of herself. You deserve respect, love and admiration.