It could be bad gas. Have you changed his food or given him new treats lately?
Could also be anal glands, as Karlin suggests. Cedar had issues with anal glands when she was only a few months old. I think it was due to pretty runny poos because her food wasnt working with her. How firm are Buddy's stools? If the smell has gone away, it could be that he managed to clear his glands on his own.
Either way -- gas or anal glands -- if he's acting normally otherwise, waiting a day or two for your appointment probably wont be a big deal.
Cedar (tri), Willow (blen), & Holly (ruby)