When I Go To The Bathroom I Only Have Gas

When I go to the bathroom I only have gas and clear liquid come out. I have been having problems for a couple of months with gas and diarrhea and have had a ultra-sound of my gall bladder and pancreas which showed nothing. Doctor wants to do a HIDA Scan but I'm think I may need a colonoscopy. Most of my gas and gas noised seem to come from my left side which leaves me thinking it's part of my colon.