Dog having a lot of gas, and vomiting?

My black lab/greyhound mix has been having gas for the past few days. I didn't think much of it, just that maybe he had eaten something out of the trash. But then today he vomited twice. It was bright yellow, so I think it was bile. Now he is having more gas, and I am starting to get worried. Could the gas and vomiting be related? Is it ok for him to have gas for several days? Nothing seems to be bothering him; he is still as active and playful as ever.