I don't think a biopsy can be 100%, but it's probably one of the closest things to a definitive diagnosis.
I'd wait and see what the results of that say, and if you want to, then go see another GI for a second opinion. That way you have all the information for another dr to look at.
32 yr old female-dx with Crohn's in '97 after emergency resection and appendectomy, 2nd resection '05, Bilateral pulmonary emboli 10/09
Currently on Humira, Omeprazole, Effexor, Seroquel, Calcium, Vit D, Coumadin