I have crohns disease and my GI suspects I now have IBS as well...I've had crohns for 14 yrs now and although fistulas are mainly linked to crohns, I'm one of the lucky (yeah right) crohnies who thankfuly have not had to deal with a fistula yet (hopefully never will).
He should be sending you in for a colonoscopy, you'll have to prep the day before for this test, cleaning your GI tract completely out.
Biggest difference between IBS and IBD is there is no inflammation what so ever with IBS but there is with IBD usually along with polyps when you have crohns and with Ulcertive colitis there is inflammation usually with ulcers...Main difference between UC and CD is that with CD the inflammation typicaly goes deeper into the intestinal walls of the affected areas which happen to be anywhere in the GI tract from the mouth to the anus...with UC inflammation and ulcers are mainly restricted to the large colon and sometimes into the anus (proctitis). Commonly CD is detected in the small bowel, usually just where it connects to the large but the inflammation or disease itself with UC is more on the surface of the lining rather then going into the lining which inturn can cause fistulas to occur as it does with CD.
I have what's called crohns/colitis which basically means my CD has set up camp where UC typically hangs out, in the large bowel (aka, the large intestine or bowel) but I also have CD in the rectom (proctitis) and in the anus known as perianal crohns skin tags....When I first became sick I had CD in the small bowel, large bowel, rectom and anus, but for the last 7 yrs it hasn't been in the small, just the other mentioned areas.
"Itis" means inflammation, hence proctITIS, colITIS, the col is abrheviated for colon.
There is an array of meds used to treat both CD and UC and often depending on the location of your disease (if in fact you have IBD) will depend on which drugs they will try on you, as some drugs reach certain parts of the intestinal tract to treat the inflammation and such.
Symptoms of both IBS and IBD (both CD and UC) are similar in regards to bathroom habits, frequency, pain, cramping, diarhea or even constipation (more so with CD constipation can occur then with UC). Blood is also a sign of either UC or CD not with IBS though. Then there's a list of extraintestinal manifestations that occur with IBD that do not typically occur with IBS, like getting osteo, arthritis, skin problems, eye inflammtion...best thing to do is google IBS and IBD and you'll be able to note all the things I havn't covered.
Good luck and take care!