10 month old 13.5 pound schnauzer mixed poodle was neutered

My 10 month old 13.5 pound schnauzer mixed poodle was neutered on Thursday and seemed to be fine other than being lethargic. He started with loss of appetite and progressed to vomiting and tarry like stools with blood in them after 2 days..
The vet gave him a prescription on Tolfedine 60 mg. but only half of a pill was to be given daily. (equalling 30 mg) when he was neutered.
I know that these are the side effects of this medication, but the vet reassures me that he is not like this due to the medication. The vet says he may have a viral infection or that maybe it could be due to something he ate. we have stopped the meds and were wondering if anyone has any insight into this.
He was already checked for Parvo.
Any help would be greatly appreciated.

Sounds like some sort of infection to me, but then I'm no vet. I would get him back to the vet asap.

clm

It could be any number of things... sometimes animals just don't feel well for a few days after surgery. 1 year old is still young but would actually be considered 'old' for a neuter surgery (where I work).. the more full grown a male dog is the more invasive the surgery is. It's not a very invasive surgery to being with, but you have to take more time as everything is fully developed.

With infections after a spay or neuter you will usually notice swelling, redness or oozing at the actual incision site.

I'm in the US and 'Tolfedine' is not available here according to google... so sorry I have no experience with it but the actual pain medication could be the cause of his symptoms more likely then the actual surgery.