as Grif said diarrhea is not normal and always a sign something is off ( indigestion, protozoa or bacterial infection), frog ( or any part of it)might be and might not be swollen,but there is a difference between soft, due to the diet, stool and actual diarrhea. yes it should be pooping a lot and very stinky if it is actual diarrhea and it might be your case, not pooping for a week and then runny stool ( and very smelly) doesn't sound good. it might be one time thing that'll just go away but it might be a bigger problem. I'd keep an eye very closely right now on a frog, keep track of what he is eating and how he is pooping, if he continue to poop very stinky and runny for a few days, get a test done asap. keep in mind you might not see it on a substrate, watch very closely!

see with frogs there might be a very fine line between being ok and run asap to the doctor situation, sometimes when you actually see a frog is not well it might be too late to go for the second option, so it is better be safe then sorry.