Anytime they vomit it is bad.
Follow Carlos' advice. Most of the time an impaction will show on the right side of the frog and I do mean the frog's right side. Since the stomach is located in this area food eaten will not be able to leave the stomach and create a bulge on this side. Vomuting can be cause by a severe impaction or the usual cause parasites and internal bacterial infections.
Either way whether the frog poops or not seek a Vet's help.