Completely random diarrhea

[Haley, Yeti, and Phin]

Sorry for the icky title but that's just exactly what we're experiencing. His potty was totally normal at breakfast and when I took him out to go after lunch he just exploded. I have no idea what could have caused this.
1.he isn't fully vaccinated so he doesn't leave our yard.
2.we haven't given him any new food or treats
3.when he goes potty we keep him on a leash and stay out there with him to monitor his behavior. It is possible he snagged something outside but I'm not sure what it could have been.

He did however get his monthly dose of flea and tick medicine on Monday. This would be his second time having it (with us) but didn't react badly to it the first time.

I have given him some pumpkin as a treat and again with dinner.

His actions ARE NOT completely normal. He is still lightly playing and chewing but is also resting a lot. Something we're not really used to. He ate dinner just fine and is drinking water. Just incase I have been giving him ice cubes to prevent dehydration.

I did call the vet and spoke with the front desk lady. while she said diarrhea is very serious, she didn't sound too worried. But if it continues I think we will probably take him in tomorrow.

Has anyone experienced this?! First time dog owner and up until now he hasn't had any problems with his stool.

Thank you so much!

[Karen, Jasper and Jackdoodle]

I would definitely bring a stool sample to the vet at the very least. 

Could he have eaten something he shouldn't have in the house? Are all socks and toys accounted for? 

[Nancy & Echo]

Hear, hear!

In this study in England, puppies from breeders and pet shops had a high incidence of gastrointestinal pathogens. http://www.ncbi.nlm.nih.gov/pubmed/23915246

Diarrhea in puppies is quite common.

Two hundred and sixty six puppies (between 5 and 14 weeks of age) from 29 French breeding kennels were included....For each puppy, fecal consistency and fecal excretion of enteropathogens (viruses and parasites) was evaluated. At least one enteropathogen was identified in 77.1% of puppies and 24.8% of puppies presented abnormal feces. http://www.ncbi.nlm.nih.gov/pubmed/25175676