People think im homeless how do i defend myself?

Unfortunately people might make rude comments, and theres not much you can do. You could disclose your illness with these people, or ignore them/take your business elsewhere. Either way you need to develop thicker skin and view these people as if they're the ones with the problem (they seem to be, because you'd think store managers would realize that your money is as green and valuable as anyone else's) I'd suggest trying to make your hair or clothes look nicer so the homeless thing can be ruled out tho.