Well, as you are discovering, some toads can be quite toxic to pets. Sometimes, it is just a issue of the toad tasting bitter, resulting in profuse drooling, but some of the species are quite toxic.
It is the secretions from the toad that are the concern.
Other symptoms of toxicity can include:
Weakness, Seizures, Fever, Vomiting, Diarrhea, and even heart rhythm problems.
So, this situation is well worth a emergency vet visit, especially because even if he didn't eat a toad, he clearly is in distress, and we can't manage his symptoms with at home therapy.
FYI: The Colorado River toad the Giant Toad are two of the most common poisonous toads in the U.S.
You can try rinsing the mouth some with a garden hose water.
You can also check for high ever by taking a rectal temperature using any digital thermometer.
Wish I could do more but hope that information helps