You're always welcome to vent here--that's part of what this site is for. I'm so sorry that you've had to deal with people who don't understand and have such limited patience.
My only suggestion comes from lots of experience. I'm determined not to lie about how I'm feeling, but I also don't want to be perpetually miserable (both for myself and for the people around me). So when somebody asks how I'm doing, I grin and very cheerfully say something like the following: "I've been better--but I guess I could be worse, too" or "Trust me, you don't want to know" or "Actually crappy, but I'll live" or "Hey, at least I'm here." If that's all they want to know, they'll just move on; if they really want to know more than that, they'll ask. Mostly they don't ask. They all tell me that they're impressed that I can maintain a sense of humor in a chronic situation--and I'm relatively satisfied because (a) I haven't lied and told them things are fine when they're not, and (b) I haven't made the mistake of revealing too many details to people who don't really want to know them. But I've left the door open to anyone who wants to know more.
This can be a very lonely disease sometimes. Sometimes it helps to write down how you feel. I wish you better days and better friends.