At least it's not beside it... If it was an impacted anal gland (which is usually bigger than you described), that would have been a really serious emergency. If the diarrhea continues or gets worse, the doggy may need to go to the vet sooner. You don't want the dog to get dehydrated.
Really try to stop the doggy from forcing too...
I just remembered-- are you in the States? Yes, eh? Because in Canada, it's a long weekend, so you'd have to wait till Tuesday to go to a regular vet...