I don't know what to tell my friend half the time?

So I have IBS and kidney problems and my friends will always ask why don't you go out or what's wrong with you not wanting to do anything? The truth is I want to go out and all that but when it's hard to sit because there's something wrong with my abdomen or ...butt then I just don't know what to say. I am embarrassed by my condition. I'm 22 and use suppositories. I mean I feel like I have to hide a secret every day and that's why I don't get close to people.