I'm sorry your feeling unwell and it never helps if you're unsure about your diagnosis either. It's difficult enough without the added extra worry - I hope your second opinion puts some of those concerns to rest.
I couldn't agree with pb4 more though. It's great advice and exactly what I've been told by my doctors too. I was diagnosed with Crohn's colitis/proctitis. Which, as pb4 explains, is Crohn's disease in the colon and the rectum/anus area of the body. Because Crohn's can affect anywhere in the digestive system, some doctors often refer to oral crohn's, small bowel crohn's, crohn's colitis or crohn's proctitus - simply to avoid any confusion - it instantly tells any medical practitioner where your particular crohn's is in the body.
My doctor told me that he could never differentiate between Crohn's and Colitis without, in the very least, a colonoscopy. Notes on symptoms alone cannot be truely accurate, although some symptoms (like erythema nodosum, pyoderma gangrenosum, and perianal complications) would tend to point more towards Crohn's, but not exclusively. As pb4 says, the inflammation in each disease looks different, is spaced differently and can cause a different pitting on the bowel wall. Have you had a colonoscopy yet? Or is that how you were originally diagnosed?
Talk over any concerns with the doctor to put your mind at rest, and either way, all the very best Micky.