I had an unsussesful colonoscopy last week. they couldn't complete due to pain from the gas/air pumped in. how common is this? what's the alternative.

Colonoscopy: incomplete colonoscopy can occur up to 5 to 10% of the time. Whether a repeat attempt would be successful mostly depends on why it was unsuccessful in the first place. You should talk to your G.I. doc about whether a repeat attempt with better sedation or a better prep would be useful. If not, a "virtual" colonoscopy might be the next step. Good luck.