I definitely agree with pb4, if you're having joint pain and inflammation AND bleeding with bowel movements, that could be a sign of IBD (crohn's or uc). Your doc should be testing you thoroughly - including asking for a colonoscopy w/biopsies. There are many ways to prep for a scope. On top of an enema, now a days you could use laxative pills, or the Fleet stuff that is only 6 small bottles, or the gallon GoLytely goo.
If, for whatever reason, you are not able to get scoped, there is always Prometheus Labs. I mailed them a few vials of blood and they tested for IBD, Celiac's and Lactose Intolerance. I'm not sure how accurate they are, but it might be worth checking out if all else fails.
Co-Moderator IBS Forum