Which doctor should I see ?

I have noticed a change in my bowel movements and I wanted to get tested for gallbladder/liver problems and things like celiacs disease, IBS, and Crohns disease. My insurance allows me to see a specialist without a referral, but I was thinking I might just see my general doctor first. Should I see him or go to the specialist (gastro)? I don't want to pay for unnecessary tests.